Cabinet will base its decision today on any alert level changes on factors including the number of cases, whether they can all be linked to existing cases, and how many close contacts there are.
The level of testing all over the country will also be important, as will whether there are any cases or close contacts outside of Auckland or the Coromandel.
There won't be any certainty about the size of the outbreak or how large it might become, and ministers will rely on the advice of director-general of health Ashley Bloomfield.
As of yesterday's 1pm update, there were 21 cases - 20 in the cluster, and one more in the community with the Air NZ aircrew member.
Since then, other cases have emerged including a patient who had been in North Shore Hospital
None of the cases have been confirmed as outside of Auckland - though the Herald understands that cases have popped up in Wellington this morning - but there could be undetected cases in other parts of the country.
That's because many of the 120-plus locations of interest would have included patrons from all over the country, including some of the tourist attractions that the Devonport tradesman went to in the Coromandel.
High testing numbers around the county would give a good indication of any cases.
There were almost 13,000 tests processed nationwide on Wednesday, though the Ministry of Health has not provided a regional breakdown.
Wastewater testing will also provide some clues, and so far no results have shown any sign of the virus outside Auckland.
Today Cabinet will consider wastewater results from Thames and the Coromandel that were taken yesterday.
Modelling by the team led by Professor Shaun Hendy estimates there could have been about 100 cases in the community at the time the first one was detected on August 17.
The unknowns about the cases so far include whether there might be more than one chain of transmission.
So far there has been no link between the probable index case - a traveller from Sydney who flew to New Zealand on August 7 - and the 20 cases in the cluster.
Yesterday Bloomfield said 12 of the cases in the cluster are connected, five are thought to be linked to Avondale College, and the remaining three are still being investigated.
There were 362 close contacts identified in yesterday's update, though that did not include those at Avondale College or those who had attended a church service on Sunday - which will push the numbers to more than 1000.
None of them so far were outside of Auckland or the Coromandel, Prime Minister Jacinda Ardern said yesterday, but some might emerge as more cases are detected.
There are still many unknowns about how large the outbreak might become.
More cases are expected, and most of the test results from the venues that could be super-spreader events - including SkyCity Casino, Avondale College, and the church service - are also yet to come back.
Advice from Bloomfield is based on a public health assessment, but Cabinet will also consider the economic impact, as well as whether there are any cracks in public compliance.
Police Commissioner Andrew Coster has said that compliance has mostly been good, though the threshold for arrests has been lowered because Delta is so much more transmissible.
Finance Minister Grant Robertson has said that the country's economic output is cut by about $1.5 billion a week when alert level 4 is imposed on the whole country.
Ardern has also said movements through alert levels will be staged, and there won't be a lurching from level 4 to level 2 or 1.
If Cabinet decides to move any part of the country to alert level 3, it would be based on a high level of confidence that there are no Delta cases there, and travel restrictions would be required to ensure none could be carried in.
There remains a lot of uncertainty, and these calls are always a finely balanced judgement based on the best information available at the time.
If there are still too many unknowns, Ardern has previously remained cautious and stuck to lockdown until more information - and more confidence about the size of the outbreak- can be gained.
The last thing she wants, as she has said repeatedly, is to yo-yo between alert levels.