Three new cases of Covid-19 surfaced last night in Waikato less than 24 hours before Cabinet ministers decide whether to move Auckland out of level 4 lockdown.
The three new cases are household members of a remand prisoner who was also announced yesterday as a positive case.
Two of the three household members attend Mangatangi School on the Hauraki Plains and one was symptomatic while in class on Thursday.
All three positive cases, and an accompanying adult caregiver, are being moved to a quarantine facility.
The school has been closed and parents have been contacted. Arrangements are being made for the students and their families to be tested.
A pop up testing centre is being set up at Wharekawa Marae in Whakatīwai and local residents with symptoms are being urged to get tested.
Epidemiologist Professor Michael Baker Baker said these cases could tip today's decision.
"Alert level two has its limitations if there is transmission, it's not really able to stamp out an outbreak."
They also highlighted the need for mask use inside schools, he said.
In level 2, students aren't required to wear masks, however Baker said a school setting allows for the virus to "spread quite quickly".
It wasn't yet clear precisely how the new cases would influence today's Cabinet decision - or whether the area of New Zealand under lockdown would now need to be extended.
There have already been calls for Waikato to join Auckland's cordon.
Cabinet ministers had already faced a tough decision, having earlier flagged an in-principle decision to move Auckland down to level 3, and the rest of the country back to less restrictive level 2 settings, at midnight tomorrow.
The call also comes after 27 new cases were reported in the community yesterday afternoon - at least three of them as-yet unlinked - on top of those confirmed in Waikato last night.
At yesterday afternoon's media conference, Prime Minister Jacinda Ardern said Auckland's hard work had "paid off", and that those still-sizeable daily numbers coming through reflected how Delta was continuing to infect people within households.
"I know that is really anxious-making for people when they see those numbers. They don't always tell the full story but it does tell us Delta's tail is long and it is hard."
Director of public health Caroline McElnay was "cautiously optimistic" that most of the outbreak – now totalling more than 1050 cases – was under control and that it was the long tail still being seen.
More cases were expected in the coming days as some of the recent cases were from large households, where contacts are expected to test positive - but they are already in isolation.
Thirteen people were in hospital, and four in ICU.
Asked if Auckland was ready for a step-down, Covid-19 modeller Professor Shaun Hendy yesterday afternoon said he'd prefer the region stay at level 4 until the cluster was stamped out.
"I'd just like to get this behind us, and there is a risk that, if we go to level 3, that we might continue to have to battle this over the next couple of months."
While the outbreak's R value – or average number of people one infected person passed the virus on to – was still likely below one, Hendy felt contact tracers still weren't in front of it.
"We are still seeing cases acquired in the community, as opposed to just households."
Level 3 would create more locations for the virus to spread, making the task for contact tracers even more difficult, and possibly increasing the rate of transmission.
"The worst-case scenario is that in a couple of weeks, things start to look like they were in New South Wales six weeks ago, where we have case numbers clearly starting to rise," he said.
"And then, however unpalatable it might be, we would have to go back to level 4. New South Wales' healthcare system isn't coping with its Delta outbreak and ours would certainly struggle."
Baker similarly warned of following Sydney's fate.
Earlier yesterday, he described a potential scenario of cases continuing to track up under alert level 3 and possibly leaking out into the rest of the country - something that had now happened anyway.
"We could even face a situation where much of the country winds up at level 3 for several months to keep a lid on the virus while we're getting our vaccination coverage up to a level where it doesn't overwhelm our health system."
Baker said the Government would be having to take a "calculated risk" - with the more optimistic scenario being that Auckland wrestled Delta under control at level 3 and then joined other regions at level 2.
"I think this is possibly the toughest call they've had to make."
It was also troubling that officials were still discovering mystery cases in Auckland, he said.
"So long as we're getting [unlinked] cases virtually every day, it means there are still undetected cases out there in the community – and these are what we have to worry about," he said.
"While each one doesn't point to a tip of an iceberg, they do potentially indicate that there are chains of transmission that we're not yet aware of."
Asked whether New Zealand could get to zero cases in the community, Ardern believed it possible but tough.
With more than 53,000 doses of the Pfizer vaccine administered on Saturday, 73.1 per cent of eligible Kiwis had now received at least their first jab.
Seventy-eight per cent of eligible Aucklanders have had their first dose.
"You can see how rapidly we are moving up through those vaccination rates - we need to keep that momentum up."