There have been no new positive Covid cases overnight, Covid-19 Minister Chris Hipkins said today, hours ahead of Cabinet's decision on the fate of New Zealand's alert-levels.

"I haven't been notified of any positive cases overnight," Hipkins told Newstalk ZB's Mike Hosking.

"We'll get the overnight bench testing results about nine o'clock this morning as they normally come in and the fact that we haven't been notified of any new cases is very encouraging. Our goal here was a short, sharp response. It looks like at this point like that's been effective. We'll have more information as the day unfolds but I'm optimistic at this point."

The latest news comes as experts debate the Government's next moves, with one prominent epidemiologist urging caution - a move to level 2.5 for Auckland - while one economist/modeller believes concerns over a community outbreak have been a possible "false alarm".

Hipkins told Hosking said he was "optimistic" the three Auckland family cases had been contained, but he was not going to pre-empt any Cabinet decision to downgrade Auckland's level-3 lockdown or the rest of NZ's level-2 alert level.

Asked by Hosking if another day of zero cases meant the country was done and could get out of the alert levels, Hipkins said: "I wouldn't go that far - there's still a few pieces of the puzzle that Cabinet will want to weigh up including the fact that we haven't got a confirmed source for this group of cases."

Hipkins told MediaWorks officials were still looking at a set of "highly unlikely" sources of the infection.

The mother in the Auckland family - one of the three positive cases - works at an airline food and laundry supplier on the airport precinct but is not airside, while the daughter, who attends Papatoetoe High School, actually showed first symptoms.

"We may never be able to nail it down," Hipkins said.

If any close contacts proved positive and the chain of transmission was clear and there was not much risk it had been passed to others, then this would make a difference to any potential changes in the alert levels.

"It came out of nowhere and there was no clearly identified source," Hipkins said in justifying the lockdown.

He told MediaWorks New Zealand's first batch of vaccinations would go ahead on Saturday. It would be ramped up over the week.

Hipkins said fewer than 100 people would be vaccinated at the weekend. These would be border workers most at risk of contracting Covid.

The latest Covid update will be officially released by the Ministry of Health at 1pm before Prime Minister Jacinda Ardern and her Cabinet meet at 3pm. Ardern is scheduled to advise the Government's decision at 4.30pm.

Cabinet will be examining a number of key issues, such as the all-important Papatoetoe High School test results and any further clues as to the source of the outbreak.

The later meeting time means ministers will have examined the most up-to-date information on the latest community outbreak and experts' advice.

As Cabinet mulls its decision, one expert is calling for the Government to place Auckland into alert level 2.5, rather than pulling the alert level back down to 1 or 2.

Epidemiologist Professor Michael Baker was optimistic about the numbers yesterday but warned that Auckland was not ready to go straight down to level 1 or 2 just yet.

Rather, reinstating "alert level 2.5" would allow Auckland to largely reopen for business, while continuing restrictions aimed at disrupting the potential Covid chain of transmission.

Economist Rodney Jones believes the lockdown has been a possible "false alarm".

"If it's zero cases again tomorrow this has been a false alarm – no worse than Northland," Jones told Stuff, referring to another recent case in which a woman tested positive for Covid after her 14 days at the Pullman Hotel managed isolation facility. That case did not lead to a community outbreak.

Jones, who has reportedly done informal modelling work for the Government, said a large number of cases were recorded in the early days in recent serious outbreaks such as those in Australia. That had not happened in the case of the Auckland family.

"You get a whole bunch of cases at the start," he told Stuff. "You get two or three cases on day one, then maybe 10 or 12 on day two, as you start to test the pool where there's likely to have been community transmission...Here we've had three then zero zero."

Today's Cabinet decision will be strongly influenced by what Hipkins has described as the "last pieces of the puzzle".

On Sunday night, Ardern said Auckland would remain at alert level 3 until at least midnight tonight – with the rest of the country at level 2 over the same period of time.

Ahead of Ardern's announcement today, all eyes will be on the Ministry of Health's 1pm update.

There have been no new community cases identified since the initial three were discovered on Sunday – heartening results after a community testing blitz in Auckland.

Although this was "very encouraging" Hipkins said it was "too soon to speculate" as to what Cabinet would decide today.

"But a day when we get zero positive tests results is always a good day," he said yesterday.

Hipkins said that testing numbers would be a key piece of information around the Cabinet table.

There were close to 15,000 swabs taken on Monday, some 10,500 in Auckland alone.

That figure was 3379 yesterday.

"This is a great response, and exactly what we need," said director-general of health Dr Ashley Bloomfield.

The results of these tests will be critical when it comes to the advice Bloomfield will provide to ministers at the Cabinet meeting.

Although he said this was "very encouraging," he would not go as far as saying New Zealand was out of the woods just yet.

That's because the Ministry of Health has dramatically increased the number of people officials consider to be close contacts of the Covid-positive family.

On Monday there were 42 close contacts of the three infected family members - but yesterday Bloomfield revealed that number had more than doubled to 109.

And of the 36 close contacts at Papatoetoe High School, 22 have yet to return negative tests.

There were again long lines at the school yesterday as student, teachers, parents and staff members waited to be tested.

Bloomfield also revealed there were now more than 2000 "casual plus" contacts the Ministry of Health are following up with.

Another key piece of information ministers will consider today is the investigation into how the disease was able to enter the community in the first place.

The running theory has been the mother, who worked at LSG Sky Chefs and handled airlines' laundry, was the first to catch Covid-19 before passing it on to her daughter and husband.

However, Bloomfield said he was remaining "open-minded" as to whether it was actually the daughter who contracted Covid-19 first.

Speaking at yesterday's 1pm update, he said that was "exactly one of the things we are trying to get to the bottom of".

Although the mother worked in close proximity to Auckland airport, he said officials were not "jumping to conclusions" that this was the root of the infection.

"Especially because the daughter's symptoms seem to have preceded the mother's."

And as Bloomfield and Hipkins faced questions from the press yesterday, so too did Ardern from the Opposition.

Question Time in a socially distanced Parliament yesterday was dominated by Covid-19.

During questioning from National leader Judith Collins, Ardern revealed she learned about the new community cases just 90 minutes before the public was informed.

Although Ardern learned of the new cases at 11am on Sunday morning, Bloomfield told the AM Show yesterday he learned about the case at 10pm the night before.

But the thrust of National's attack was around saliva testing – the party wants the Government to mandate this type of testing every day at all MIQ facilities.

Speaking in the House, Ardern said saliva testing was already underway in "high-risk areas," such as the Jet Park Hotel.

But she said saliva testing is not as accurate as the standard nasal swab test and thus could not be used by itself to detect Covid-19.

Meanwhile, Hipkins revealed that the Government has made major changes to MIQ facilities.

Air filtration systems in all facility lifts are being replaced, CCTV systems have been upgraded and people's movements have been further limited

The changes were made following an investigation at the Pullman Hotel facility after a number of people in the community tested Covid-positive after staying there.

After being temporarily closed, the facility is once again open – albeit at 50 per cent capacity – and just the lower floors will be occupied for the first two weeks.