Zimbabwe military officers read an address live on state TV in the early hours of Wednesday, saying President Robert Mugabe was safe and that the country was not undergoing a coup.

"It is not a military takeover of government," said one general reading a statement. "We wish to assure the nation that his excellency the president... and his family are safe and sound and their security is guaranteed."

The army said it was "targeting criminals around" Mugabe and urged people to remain calm, the Daily Telegraph reports.

"As soon as we have accomplished our mission we expect that the situation will return to normalcy."

The address came hours after several loud explosions echoed across central Harare and troops seized the state broadcaster.

The developments in the Zimbabwe capital fuelled speculation that a coup was under way against Mr Mugabe, after the head of the armed forces threatened to "step in" over the sacking of an influential vice president.

Zimbabwe's ruling party accused General Constantine Chiwenga of treason over his comments, after the rare appearance of the military vehicles in Harare.

Gunfire erupted near Mr Mugabe's private residence in Harare in the early hours of Wednesday, a witness told AFP.

"From the direction of his house, we heard about 30 or 40 shots fired over three or four minutes soon after 2.00 am," a resident who lives close to Mugabe's mansion in the suburb of Borrowdale said.

Armed soldiers were assaulting passers-by in the early morning hours in Harare, according to the Associated Press, while soldiers were seen loading ammunition near a group of four military vehicles.

Aggressive soldiers told passing cars to keep moving through the darkness. "Don't try anything funny. Just go," one told a Reuters reporter on Harare Drive.

Two hours later, soldiers overran the headquarters of the ZBC, Zimbabwe's state broadcaster and a principal Mugabe mouthpiece, and ordered staff to leave. Several ZBC workers were manhandled, two members of staff and a human rights activist said.

Shortly afterwards, three explosions rocked the centre of the southern African nation's capital, near the University of Zimbabwe campus, witnesses said.

The US embassy in Zimbabwe warned its citizens in the country to "shelter in place" due to "ongoing political uncertainty".

The UK embassy in Harare also urged British citizens to stay indoors during the "uncertain situation".

The Ministry of Foreign Affairs and Trade has urged New Zealanders in Zimbabwe to stay indoors.

"There is ongoing political uncertainty in Zimbabwe. The security situation is unpredictable. There are reports of intensified security activity in the capital Harare, including the use of military vehicles.

"New Zealanders currently in Harare are advised to stay indoors in a safe place and to remain vigilant. You should monitor local and international media to stay informed of developments and safety and security risks."

Tensions have been building in Zimbabwe since Emmerson Mnangagwa, a powerful figure in the ruling Zanu-PF party, fled to South Africa last week after he was fired and was then stripped of his lifetime membership of the party.

The move was widely seen as part of a battle between Mnangagwa and Grace Mugabe, the first lady, over the presidential succession when Mr Mugabe dies or steps down. The Zimbabwean president, who is 93, fights his last election next year.

Many expect Mrs Mugabe to be appointed vice president in Mnangagwa's place at the Zanu-PF special congress next month.

Chiwenga, an ally of Mnangagwa, demanded on Monday that Mugabe immediately cease "purging" the former vice president's allies in the party and in government.

"We must remind those behind the current treacherous shenanigans that when it comes to matters of protecting our revolution, the military will not hesitate to step in," the head of the armed forces commander said.

In a statement issued on Tuesday evening, Zanu-PF accused Chiwenga of "treasonable conduct."

Earlier on Tuesday Kudzai Chipanga, the leader of Zanu-PF's youth wing, accused Chiwenga of stealing billions of rands and said his movement would act to protect the president.

"We as Zanu-PF youth league are a lion which has awakened and found its voice, therefore we will not sit idly and fold our hands whilst cheap potshots and threats are made against Mugabe," he said in a statement widely released on social media.

The governments of South Africa and Zambia on Tuesday warned military leaders in Harare not to take any "unconstitutional" steps to avenge Mnangagwa.

Senior military sources in Johannesburg and Pretoria said they warned Chiwenga to avoid any "disruption to the constitution" after the military convoys were spotted on Tuesday afternoon.

South African diplomatic sources said late Tuesday that Zambian president Edgar Lungu also warned Chiwenga to ensure that Zimbabwe's constitution was respected.

Reports from military sources in Harare said: "We are in control," without giving more detail.

A source living close to Mugabe's mansion said: "We presume any coup plotters would know that Zimbabwe would run out of fuel in a week or so, and that South Africa would likely cut off electricity. Zimbabwe is a landlocked country and cannot survive if all borders were closed."

A military intervention in Zimbabwean politics would be fraught with difficulties.

The African Union and the regional 15-nation Southern African Development Community are both on record that they do not recognise any authority which comes to power via a coup d'etat.

This article originally appeared on the Daily Telegraph and is reproduced with permission.