Explosions have rocked several Ukraine cities, including the capital Kyiv, as Russia launches "full-scale war", says the Ukrainian Government.

Russian President Vladimir Putin declared a "special military operation" but the Ukraine Interior Ministry said the Russian invasion had started. Ukraine's Foreign Minister Dmytro Kuleba called it "full-scale war".

US president Joe Biden and other western leaders have condemned Russia's move – but Putin warned them that any attempt to interfere with the Russian action would lead to "consequences they have never seen."

He said the attack was needed to protect civilians in eastern Ukraine – a claim the US had predicted he would falsely make to justify an invasion. In a televised address, Putin accused the US and its allies of ignoring Russia's demand to prevent Ukraine from joining NATO and offer Moscow security guarantees.

Ukraine President Volodymyr Zelenskyy has declared the country is under martial law. Just after 6pm NZT, the people of Ukraine began waking up to the Russian invasion. Sirens sounded in Kyiv, warning the population that the city is under attack, as explosions could be heard in the distance.

Here's Zelensky's full statement:

"Dear Ukrainian citizens, this morning President Putin announced a special military operation in Donbas. Russia conducted strikes on our military infrastructure and our border guards. There were blasts heard in many cities of Ukraine. We're introducing martial law on the whole territory of our country. A minute ago I had a conversation with President Biden. The US have already started uniting international support. Today each of you should keep calm. Stay at home if you can. We are working. The army is working. The whole sector of defense and security is working." "No panic. We are strong. We are ready for everything. We will win over everybody because we are Ukraine."

It comes after Ukraine declared a state of emergency over the unfolding crisis with Russia, and Putin sparked panic by recognising the breakaway territories of Luhansk and Donetsk in eastern Ukraine – known collectively as the Donbas region – earlier this week.

In a televised address to the Russian people, the president said clashes between Ukrainian and Russian forces were "inevitable" and "only a question of time". 

Today, Ukraine woke up to a Russian invasion. 

CNN reported explosions in Kyiv early on Thursday afternoon, NZT. 

"This is the first time we have heard anything like this in the years I have been reporting here," says CNN reporter Matthew Chance as he dons a flak jacket. 

CNN also reported a series of blasts heard in the city of Kharkiv 480km to the east of Kyiv, and there were also reports of explosions near the port city of Mariupol. Residents in the city, which is located in south eastern Ukraine, were woken up at 3.30am local time by blasts 50km from the Russian border. 

'No one is running away' 

Dmytro Kuleba, Ukraine's Minister of Foreign Affairs, today told Ukrainians that the country is fighting. 

To Ukrainians around the globe: Putin attacked, but no one is running away. Army, diplomats, everyone is working. Ukraine fights. Ukraine will defend itself. Ukraine will win," he wrote on Twitter. 

"Share the truth about Putin's invasion in your countries and call on governments to act immediately." 

Meanwhile, reports state that Nato members in eastern Europeans are invoking Article 4 to allow for "urgent consultations on military plans for the alliance". 

Ukraine attacked through multiple borders 

CNN reports Ukraine was attacked through multiple borders. 

The Ukrainian state border service said "At about 5:00 a.m., the state border of Ukraine in the area with the Russian Federation and the Republic of Belarus was attacked by Russian troops supported by Belarus," 

It added that attacks are being carried out in Luhansk, Sumy, Kharkiv, Chernihiv and Zhytomyr regions — areas on the eastern and northern borders of Ukraine. The attacks are targeting border units, border patrols and checkpoints using artillery, heavy equipment and small arms, the border service said. 

"In addition, the attack takes place from the Autonomous Republic of Crimea side," said the service. 

Video footage appeared to show clouds of smoke rising up into the night sky near Mariupol, but it was unconfirmed whether it was as a result of shelling. 

Flights of civil aircraft across Ukraine airspace have been suspended as the country shifted to a war footing, declaring a state of emergency, beginning to mobilise reservists and calling on its citizens to immediately leave Russia amid warnings of an imminent full-scale invasion. 

A post on Twitter claimed to show images from the Kalanchak outpost of soldiers "running away". 

The post read: "Kalanchak outpost is under attack. Ukrainian soldiers and civilians are running away." 

Europe's top air traffic authority is urgently telling airlines and other civilian flights to stay away from Ukrainian airspace. 

CNN reported that UN Secretary General Antonio Guterres sent a message to Putin to "stop your troops from attacking Ukraine. Give peace a chance. Too many people have already died". 

CNN has also reported a ground invasion is underway from Belarus.

Explosions recorded in several cities across Ukraine 

Robert Ayson, Centre for Strategic Studies at Victoria University, said there had been reports of explosions in several Ukrainian cities. 

If troops were moving to the south, Ayson suggested that Russia could be trying to cut off Ukraine's access to the Black Sea. 

Putin clearly wanted Ukraine to not have anything to do with the West, Ayson told Newstalk ZB. 

"He hasn't been able to get what he wants through threats and intimidations and now he's using force," Ayson said. 

Putin believed Russia was boss in that part of the world and that Ukraine needed to heed that, Ayson said. 

Ayson believed the situation was "well beyond the attack on Eastern Ukraine area...we look to be closer to a full-blown invasion". 

'The world will hold Russia accountable' 

US President Joe Biden says "The world will hold Russia accountable". 

"President Putin has chosen a premeditated war that will bring a catastrophic loss of life and human suffering." 

Biden condemned Russia's "unprovoked and unjustified attack". 

Biden has said he will work with Nato to coordinate a response but has emphasised the US will not send American troops to Ukraine. 

Read Joe Biden's full statement below: 

"The prayers of the entire world are with the people of Ukraine tonight as they suffer an unprovoked and unjustified attack by Russian military forces. President Putin has chosen a premeditated war that will bring a catastrophic loss of life and human suffering. Russia alone is responsible for the death and destruction this attack will bring, and the United States and its Allies and partners will respond in a united and decisive way. The world will hold Russia accountable. "I will be monitoring the situation from the White House this evening and will continue to get regular updates from my national security team. Tomorrow, I will meet with my G7 counterparts in the morning and then speak to the American people to announce the further consequences the United States and our Allies and partners will impose on Russia for this needless act of aggression against Ukraine and global peace and security. We will also coordinate with our NATO Allies to ensure a strong, united response that deters any aggression against the Alliance. Tonight, Jill and I are praying for the brave and proud people of Ukraine." 

Canadian Prime Minister Justin Trudeau called the invasion of Ukraine an "egregious attack". 

Russian military tanks advance in the Russian separatist-controlled part of the Donbas region on February 23, 2022. Photo / Getty Images 

Meanwhile, the Kremlin said rebels in eastern Ukraine asked Russia for military assistance Wednesday to help fend off Ukrainian "aggression," an announcement that immediately fuelled fears that Moscow was offering up a pretext for war, just as the West had warned about. 

A short time later, the Ukrainian president rejected Moscow's claims that his country poses a threat to Russia and warned that a Russian invasion would cost tens of thousands of lives. 

"The people of Ukraine and the government of Ukraine want peace," President Volodymyr Zelenskyy said in an emotional overnight address to his nation in Russian. "But if we come under attack, if we face an attempt to take away our country, our freedom, our lives and lives of our children, we will defend ourselves. When you attack us, you will see our faces, not our backs." 

Zelenskyy said he asked to arrange a call with Russian President Putin late Wednesday, but the Kremlin didn't respond. 

In an apparent reference to Putin's move to sanction the deployment of the Russian military to "maintain peace" in eastern Ukraine, Zelensky warned that "this step could mark the start of a big war on the European continent." 

"Any provocation, any spark could trigger a blaze that will destroy everything," he said. 

He challenged the Russian propaganda claims, saying that "you are told that this blaze will bring freedom to the people of Ukraine, but the Ukrainian people are free." 

Kiwis flee Ukraine 

There are currently 23 New Zealanders registered on SafeTravel as being in Ukraine, the Ministry of Foreign Affairs said earlier today. 

A total of 17 Kiwis have fled the country since Foreign Affairs Minister Nanaia Mahuta warned New Zealanders in Ukraine to "leave immediately" on February 12. 

MFAT urged Kiwis to not travel to Ukraine due to the risk of an armed conflict, or to leave if they were there. 

"The security situation in Ukraine could change at short notice and New Zealanders should not rely on support with evacuating in these circumstances." 

Foreign Minister Nanaia Mahuta is on a trip to the United Kingdom and Europe. Earlier today, during a meeting with a UK MP, she reiterated her support "for Ukraine's sovereignty and territorial integrity and call on Russia to uphold the International rule of law". 

Stock markets worldwide fall after Putin's declaration of war 

Markets around the world fell on the back of news. The NZX, down 1.93 per cent just after 4pm, had fallen further to 2.15 per cent in the red as of 4:30pm. 

The invasion of Ukraine is also set to have an impact on oil prices. 

The United Nations Security Council quickly scheduled an emergency meeting Wednesday night at Ukraine's request. Ukrainian Foreign Minister Dmytro Kuleba called the separatists' request "a further escalation of the security situation." 

Anxiety about an imminent Russian offensive against its neighbour soared after Putin recognised the separatist regions' independence on Monday, sanctioned the deployment of troops to the rebel territories to help "maintain peace" and received parliamentary approval to use military force outside the country. The West responded with sanctions. 

Kremlin spokesman Dmitry Peskov said the rebel chiefs wrote to Putin Wednesday, pleading with him to intervene after Ukrainian shelling caused civilian deaths and crippled vital infrastructure. 

White House press secretary Jen Psaki said the separatists' request for Russian help was an example of the sort of "false-flag" operation that the US and its allies have expected Moscow to use as a pretense for war. 

"So, we'll continue to call out what we see as false-flag operations or efforts to spread misinformation about what the actual status is on the ground," she said. 

The US and key European allies accused Moscow of crossing a red line Tuesday in rolling over Ukraine's border into a separatist eastern region known as the Donbas, with some calling it an invasion. 

The app of the Russian government newspaper is displayed on an iPhone screen showing Russian President Vladimir Putin during his speech in the Kremlin. Photo / AP 

Earlier in the day, Ukrainian lawmakers approved a decree that imposes a nationwide state of emergency for 30 days starting Thursday. The measure allows authorities to declare curfews and restrictions on movement, block rallies and ban political parties and organizations "in the interests of national security and public order." 

The action reflected increasing concern among Ukrainian authorities after weeks of trying to project calm. The Foreign Ministry advised against travel to Russia and recommended that any Ukrainians who are there leave immediately. 

Russia on Wednesday evacuated its embassy in Kyiv as hopes for a diplomatic way out of a new, potentially devastating war in Europe waned. 

"For a long time, we refrained from declaring a state of emergency ... but today the situation has become more complicated," National Security and Defense Council head Oleksiy Danilov told parliament, emphasizing that Moscow's efforts to destabilise Ukraine represented the main threat. 

Pentagon press secretary John Kirby said the Russian force of more than 150,000 troops arrayed along Ukraine's borders is in an advanced state of readiness. "They are ready to go right now," Kirby said. 

A demonstrator holds a placard saying 'Ukraine will never surrender' as he attends a protest outside the Russian Embassy, in London. Photo / AP 

The latest images released by the Maxar satellite image company show Russian troops and military equipment deployed within 10 miles of the Ukrainian border and less than 50 miles from Ukraine's second-largest city, Kharkiv. 

In response to Russia's action, President Joe Biden allowed sanctions to move forward against the company that built the Russia-to-Germany Nord Stream 2 gas pipeline and against the company's CEO. 

"Today, I have directed my administration to impose sanctions on Nord Stream 2 AG and its corporate officers," Biden said in a statement. "As I have made clear, we will not hesitate to take further steps if Russia continues to escalate." 

Germany said Tuesday it was indefinitely suspending the project, after Biden charged that Putin had launched "the beginning of a Russian invasion of Ukraine" by sending troops into the separatist regions. The pipeline is complete but has not yet begun operating. 

Putin said Tuesday he hadn't yet sent any Russian troops into the rebel regions contrary to Western claims, and Donetsk rebel leader Denis Pushilin insisted Wednesday there were no Russian troops in the region even though a local council member claimed the previous day they had moved in. 

Ukrainian Minister for Digital Transformation Mykhailo Fedorov said a wave of denial-of-service attacks targeted official websites and some banks Wednesday. The attacked knocked offline the sites of the parliament, cabinet and Foreign Ministry and caused interruptions or delays to the sites of the defense and interior ministry, which controls the police. 

Already, the threat of war has shredded Ukraine's economy and raised the specter of massive casualties, energy shortages across Europe and global economic chaos. 

Even as the conflict took a new, dangerous turn, leaders warned it could still get worse. Putin has yet to unleash the force of the 150,000 troops massed on three sides of Ukraine, while Biden held back on even tougher sanctions that could cause economic turmoil for Russia but said they would go ahead if there is further aggression. 

The satellite image provided shows artillery, troops and logistics deployment near the town of Malakeevo, Russia, approximately 20 miles from the Ukraine border. Photo / Maxar Technologies 

In other developments, Kyiv recalled its ambassador to Russia and considered breaking all diplomatic ties with Moscow; dozens of nations further squeezed Russian oligarchs and banks out of international markets; the US repositioned additional troops to NATO's eastern flank bordering Russia; and the top US diplomat cancelled a meeting with his Russian counterpart. 

European Union sanctions against Russia took effect, targeting several companies along with 351 Russian lawmakers, who voted for a motion urging Putin to recognise the rebel regions, and 27 senior government officials, business executives and top military officers. 

The Russian Foreign Ministry has shrugged off the sanctions, saying that "Russia has proven that, with all the costs of the sanctions, it is able to minimize the damage." 

In Ukraine's east, violence spiked again. One Ukrainian soldier was killed and six more were injured after rebel shelling, the Ukrainian military said. Separatist officials reported several explosions on their territory overnight and three civilian deaths. 

Russian armoured vehicles are loaded onto railway platforms at a railway station in the region not far from the Russia-Ukraine border. Photo / AP 

Facing a barrage of criticism at the 193-member United Nations General Assembly, Russia's UN ambassador Vassily Nebenzia warned Ukraine that Russia will monitor the cease-fire in the east and emphasized that "no one intends to go softly, softly with any violators." 

"A new military adventure" by Kyiv "might cost the whole of Ukraine very dearly," he warned ominously. 

After weeks of rising tensions, Putin's steps this week that dramatically raised the stakes. He recognized the independence of those separatist regions, a move he said extends even to the large parts of the territories now held by Ukrainian forces, and had parliament grant him authority to use military force outside the country. 

Putin laid out three conditions that he said could end the standoff, urging Kyiv to recognize Russia's sovereignty over Crimea, the Black Sea peninsula that Moscow annexed from Ukraine in 2014, to renounce its bid to join NATO and to partially demilitarise. Ukraine long has rejected such demands. 

- additional reporting AP