New Zealand's three new community Covid cases have identified as the UK variant of the virus and they have not been linked to any managed isolation or quarantine case, Prime Minister Jacinda Ardern said today.

But she said it was too soon to say whether Auckland would come out of level-3 lockdown - or New Zealand out of alert level 2 - as early as Wednesday night.

Auckland moved to level 3 for at least three days at 11.59 last night, with employees asked to work from home, students urged to stay away from school and police setting up checkpoints at eight locations at the region's border overnight.

Officers are checking all vehicles arriving and leaving Auckland to ensure there is no non-essential travel. Alert level 2 is less restrictive. (The full list of rules are detailed below).

Ardern told Newstalk ZB's Mike Hosking today that the link to the British variant had led officials to think the virus might have come through airport transit or it had stemmed from an international airline crew member.

There are three new Auckland community cases - a mother, father and daughter from Papatoetoe. The mother works at LSG Sky Chefs, where she handles laundry from international flights.

"We do still have people who transit through New Zealand and fly on to other destinations. They stay airside but of course, it means they are using the things that go through the laundry at this individual's place of work," Ardern told Newstalk ZB.

"The other possibility is that it's international airline crew... they also do the laundry of a couple of international airline crew. And so, that is also one of the possibilities."

It was still possible - but unlikely - the new cases had come from an MIQ case which hadn't been sequenced, said Ardern.

She told MediaWorks that the "worst-case scenario" was that the outbreak was linked to a case which had come through MIQ three or four weeks ago. That would imply a long chain of transmission - the genomic testing results this morning ruled that out.

She told Newstalk ZB that the news of the UK variant didn't necessarily mean Auckland would spend longer in level 3.

Health officials were looking into cases in Australia to see if there was a link there and she told RNZ that officials would also be contacting international airlines to check their crews' infections to try to trace the source.

Ardern said the most likely scenario was always human to human but it was important to rule out as many avenues as possible - even if they never found the source.

The key to the decision whether to shift alert levels would be whether it appeared there would be limited community spread. She said Cabinet opted for the three-day lockdown in a "very genuine way".

Ardern told Newstalk ZB that officials would look to ramp up testing up today. As soon as negatives started coming through they could start to have some confidence the virus had been contained.

She said sewage testing in south Auckland on February 10 had not shown up any Covid in wastewater, "so that gives us another bit of a layer" in a decision.

Ardern said she didn't think the latest cases were another failure to test border workers. Even if the woman was tested on February 1 as part of her fortnightly cycle - she was instead tested on February 5 after taking annual leave - her case might not have been picked up. The testing ran hand in hand with education programmes and the key was getting tested as soon as they were symptomatic.

It was "too soon to make a judgement" either way about what decision would come Wednesday but it was the right decision to lockdown Auckland because it was confirmed the family had the UK variant, said Ardern.

Police set up road-blocks

Meanwhile, police have already set up road-blocks at eight locations on Auckland's border and are checking vehicles coming into and leaving the region this morning.

Cars on the Southern Motorway were bumper-to-bumper in some spots last night as many residents looked to flee the lockdown.

"Eight checkpoints on the outskirts of Auckland will be stopping vehicles and questioning drivers, ensuring there is no non-essential movement through the region," said Police Commissioner Andrew Coster. "From midnight, anyone attempting to travel across the regional boundaries should expect to be stopped and asked for proof of essential travel. The exemption process will run the same way as it has previously."

It is expected travellers will be given some leeway today.

Ardern urged people to limit their travel and said she would be asking all her Auckland-based MPs to remain in the city.

Meanwhile, Australia has suspended its quarantine-free travel bubble for New Zealanders arriving into the country. Kiwis will now have to quarantine for 14 days. The situation will be reviewed in three days.

The dramatic developments came as the Auckland family - the mother, father and daughter - tested positive for Covid-19 and are considered community cases.

The daughter attends Papatoetoe High School and a testing site is being set up there today. The school is closed today and tomorrow.

In an emergency press conference last night, Ardern confirmed Auckland would be at alert level 3 as of 11:59pm. It will stay at this level for at least three days, and Cabinet will review the setting every 24 hours.

Another press conference will be held at 4pm today.

The rest of the country has moved to alert level 2 for the same period of time – until midnight Wednesday.

RULES AT A GLANCE LEVEL 3: Auckland
- Stay at home and work remotely if possible
- Schools and daycare can open but parents encouraged to keep children home
- Gatherings restricted to 10 people, but only for weddings and funerals
- Travel restrictions with borders around Auckland
- Public venues such as libraries, pools and playgrounds closed

LEVEL 2: Rest of New Zealand
- People can still go to work
- Schools and daycare remain open
- Gatherings restricted to 100 people
- Travel into Auckland restricted

Ardern said she was asking Aucklanders to stay home as it is the "right thing to do". "We have stamped out the virus before, and we will do it again."

The call was made by Cabinet after an emergency meeting on Sunday.

Mother, father and daughter test positive

The moves have been sparked by the emergence of the three new community cases in the family, who live in South Auckland's Papatoetoe.

Director-General of Health Ashley Bloomfield believes the mother – who works at airline supplier LSG Sky chefs in Mangere – was the first to contract the disease. She works directly with laundry from aircraft.

There are still many unknowns and officials will work around the clock to find answers, including how the mother contracted the virus.

Ardern said the Government had again decided to go hard and early, as it was a tactic which had worked well in the past.

The new level 3 rules in Auckland meant everyone who was not an essential worker should stay home. That means schools across the city will be closed.

Ardern said supermarkets and petrol stations would remain open; she told Aucklanders there was "no need to rush out and get essential items".

The level-3 rules mean that the Prada Cup racing that had been scheduled for Wednesday between Luna Rossa and Ineos Team UK has been postponed.

And any other event over scheduled to go ahead in the next three days will also have to be cancelled. Level 3 restrictions mean there can be no gatherings of more than 10 people unless they are for weddings funerals and tangihanga.

That number is 100 for the rest of the country, but both Ardern and Bloomfield were advising people to "be vigilant".

Over the coming days, Ardern said officials would be working to figure out as much about the new cases as possible.

That includes undergoing another testing blitz in Auckland to find out how extensive the community transmission may have been.

Testing at Papatoetoe High School

A focal point will be on Papatoetoe High – the school that the daughter, one of the new confirmed Covid cases - attends.

Papatoetoe High School principal Vaughan Couillault said yesterday the pupil had only been at school for one day last week.

Ardern said the Government was taking no chances – it has set up a pop-up testing station for students, parents, teachers and staff members to be tested.

There are 1400 students at the school.

And as the testing blitz begins, so too does the investigation into how the mother contracted Covid-19.

Although she worked at LSG Sky Chefs – one of the world's largest airline catering providers – Bloomfield revealed the woman did not handle any food and it was mostly laundry.

She was receiving regular tests every two weeks but, as she was on annual leave, she did not have one more recently.

"Our understanding is they were tested on January 18 – that would have meant they would have been retested on the February 1 but they were on annual leave during that period," Ardern said.

That means the next time they were tested was when they were symptomatic.

Ardern said those testing regimes – which are the job of the employer – "should be maintained" and this is something the Government will be looking into.

Bloomfield said it was too soon to say much about the case, as officials were still doing the genomic sequencing.

But he said it was likely either the South African, or UK variants.