An Auckland University Professor of Medicine says that the latest cases highlighted the country had not had a proper debate about the level of acceptable risk around alert levels.

Prime Minister Jacinda Ardern yesterday said she was asking Aucklanders to stay home as it is the "right thing to do", after three new cases with Covid-19 from an unknown source appeared in the community.

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

Howeverm Des Gorman told Kate Hawkesby that other recent cases had not sparked this level of response.

"Why are we still isolating high-risk returnees in the middle of our largest city? This is simply nuts. We are putting our livelihoods and wellbeings at risk because we are simply not managing the level of risk that we currently have appropriately. We haven't thought through the risk we are prepared to live with. If level 3 is the right reponse then they shouldn't have been quarantined in Auckland."

He says it seems to be a case by case reaction, which is not shaped by "any underlying logic". 

Gorman says the outcome of the genome sequencing will be crucial.

"Genomically, you can link this case in South Auckland to a known case at the border, than you can be a lot more confident that there are not missing vectors of transmission operating out there."

Politicians react

Leader of the Opposition Judith Collins and Act leader David Seymour criticised the Government for putting Auckland into another lockdown.

Collins, who is returning to Wellington while her Auckland MPs stay put in Tāmaki Makaurau, said the latest lockdown move will be a "devastating blow" for New Zealanders.

"This will be difficult news for all New Zealanders.

"I feel for the people who have already sacrificed their livelihoods, their jobs and their businesses to keep Covid-19 out."

Collins urged people to stay vigilant in the fight against Covid-19 and follow the advice of health officials.

Finding the source of the outbreak and vaccinating border workers was a matter of urgency, she said.

She said if this proves to be another border failure that is unacceptable.

New Zealand is preparing for the arrival of the first batch of Covid-19 vaccines this week. Ardern announced on Friday that frontline Covid-19 workers will get the vaccines first.

After those roughly 12,000 workers are vaccinated, their close family will be offered the jab.

Collins said National has been calling for an accelerated rollout of vaccinations for border workers and frontline staff since January.

"We were acutely aware of the economic and social damage a third lockdown could cause. Avoiding this very scenario at all costs should have been the Government's top priority."

Collins attended the 22nd Big Gay Out in Auckland, after Ardern had to ditch her appearance at the event to race to Wellington in the wake of three new community cases.

Seymour said it "was only a matter of time before an outbreak forced another lockdown".

He called New Zealand a "sitting duck, saved by luck, citizen cooperation and geographic isolation".

"The Government did not take the opportunity to strengthen our defences with better testing and contact tracing, as the Prime Minister claimed. Instead it pinned its hopes on a vaccine while inviting the Wiggles through MIQ.

"We must hope that the Government's testing and tracing can isolate this outbreak before a damaging extended lockdown harms livelihoods."

"Last month the Government tried to say New Zealand's position was so good we could afford to wait for a vaccine. Act said at the time that we are only an outbreak away from wishing we had one.

Ardern took to Facebook Sunday evening to answer questions from Kiwis on the alert level move.

"Basically, what we want everybody to do is stay home," she said.

"We are asking people from Auckland not to leave."

But there are some exceptions such as those that live on or near the Auckland border needing to travel into the region for legitimate purposes.

She said anyone who got an exemption last time can anticipate getting one this time.