Prime Minister Jacinda Ardern has given her assurance the government will consider helping businesses should Auckland's three -day level 3 lockdown be extended, Mayor Phil Goff says.

Prime Minister Jacinda Ardern announced last night Auckland would move to alert level 3 from 11.59pm on Sunday while the rest of the country would move to level 2.

The move is in response to three new community cases, announced yesterday afternoon.

They are a mother, father and daughter who live in the South Auckland suburb of Papatoetoe. Another household contact has tested negative. The mother works for laundry and catering company LSG Skychefs, which services planes at the airport, but the source of her infection is not yet known.

Results from the genomic testing were expected late on Sunday evening and the Ministry of Health is expected to provide an update on the results today.

The move to level 2 and 3 will remain in place for three days, with Cabinet reviewing the situation every 24 hours, Ardern said.

"Three days should give us enough time to gather further information, undertake large scale testing and establish if there has been wider community transmission," Ardern said.

She will provide another update at 4pm today, following a Cabinet meeting.

Another lockdown 'won't come as a surprise'

For most of the country schools and businesses remain open, but people are encouraged to keep track of where they have been and stay home if they are unwell.

Masks are mandatory on public transport and encouraged where physical distancing isn't possible. Gatherings, including weddings and funerals, are limited to 100 people.

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For Aucklanders, the rules are tougher.

Schools will be open for the children of essential workers only.

The official advice is people should work from home if they can.

If you leave your home, you should keep your distance from other people, and wear a mask if possible.

All public venues, including libraries, museums, gyms and cinemas, will shut.

A queue formed outside the Grey Lynn Countdown in Auckland shortly after it was announced the city would be moving to alert level 3 Photo: RNZ/ Simon Rogers

Supermarkets and pharmacies will stay open, and people are encouraged not to panic buy - although there were long queues reported at some supermarkets in Auckland last night.

Central Auckland resident Vicky said the government was doing the right thing by increasing alert levels.

"As long as everybody does what they're told we're pretty confident that we'll tackle it the same way it has been done the last two times."

Auckland Mayor Phil Goff Photo: RNZ / Dan Cook

Auckland Mayor Phil Goff believed Aucklanders wouldn't be stunned at the sharp lockdown.

Goff said he hoped all close contacts of the cases tested negative and the lockdown would not need to drag on.

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"Nobody is ready for it in the sense that they want it, but they're probably ready for it in the sense that everybody understood that while we've done better than every other country in the world, we are living in a world that is absolutely rampant with Covid-19," he said.

"So it won't come as a surprise. It won't be welcomed, and I think overwhelmingly, I think New Zealanders understand if we respond hard and quickly that's the best way to stop the spread of community transmission of Covid-19."

While he appreciated the impact the lockdown would have on people's lives and businesses around the city, he said it made sense.

"We know that we cannot afford to let this spread out into the community because the human, the health and the economic cost will be far much greater."

'Major blow for restaurants'

The announcement of a return to levels 2 and 3 was another blow for an industry already struggling for survival, Restaurant Association CEO Marisa Bidois said.

"Obviously this is a major blow for our industry who are already struggling to recover from the compounded impact of changes to alert levels and border closures. With borders closed, our revenues continue to suffer and these changes of alert levels are incredibly difficult to manage.

"Many businesses will have stocked up on food for the days ahead and will now incur wastage costs on top of significantly reduced revenues.

However, Bidois said the industry would far prefer a short time at level 3 than extended lockdowns seen overseas.

Goff said Ardern has given her assurance the government would consider helping businesses should the three day level 3 lockdown be extended.

"We have an assurance from the prime minister should this level 3 restriction have to go beyond 72 hours, three days, then the government will look at providing assistance to businesses where that is needed."

Travel restrictions in and out of Auckland

There will be eight police checkpoints on the outskirts of Auckland. Police will stop vehicles and question drivers, ensuring there is no non-essential movement through the region.

The checkpoints will mostly be in the same locations as last time Auckland was in lockdown, police said.

Ardern said people who live in Auckland but are currently away, can return; and anyone who's in Auckland now but does not live there, can leave.

File photo: A police checkpoint at the southerb boundary in Auckland, in August 2020. From Monday there will be eight police checkpoints on the outskirts of Auckland during alert level 3. Photo: AFP

Christchurch resident Jan said trying to get home after spending the weekend in Auckland had now become much more complicated.

"It's a moving situation. We managed to get a flight tomorrow but it might be leaving tonight."

People transiting through the region will be allowed to do so, and those who live just outside Auckland but need to enter for legitimate reasons, will also get through the border checkpoints.