The Government will meet on Friday to decide whether to keep the country in level 4 lockdown, as the numbers of cases and exposure sites swell.

Two experts spoken to by Stuff said it was very likely the Government would extend the level 4 settings for at least the weekend, as much about the size of the cluster was still not known.

The Government will announce the decision at 3pm after meeting at 1pm and receiving new case numbers then.

It has already been signalled that Auckland the Coromandel will remain in level 4 lockdown until at least Wednesday, but the restrictions on the rest the country are due to expire at midnight.

As at 1pm on Thursday, the community cluster had grown to 20, with another unrelated community case connected to the border.

More than 140 locations of interest had been announced as linked to known cases on Thursday night. The positive cases included students at two large Auckland high schools and a teacher at a third.

Prime Minister Jacinda Ardern had indicated that even if the rest of the country did move down, it would be slowly through the alert levels – not a sudden return to normality.

Ardern had some good news to share with the country on Thursday, as the Government confirmed the Covid-19 variant infecting people in the North Shore was closely matched to Covid found in a recent returnee from Sydney in managed isolation.

“Now we can be fairly certain how and when the virus came into the country,” Ardern said.

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“Based on timelines, there are minimal, possibly only one or maybe two, missing links between this returnee and the cases in our current outbreak, and the period in which cases were in the community is relatively short.”

Yet the high number of locations visited by the community cases, and the infectiousness of the Delta strain, mean New Zealand is not out of the woods yet, experts say.

University of Auckland Covid-19 modeller Shaun Hendy said the small period of time between the virus arriving in the country and being found meant there was less to worry about “upstream”.

“The relatively recent date of that person's arrival really cuts down the amount of time that it has been in the community. That will make it easier to contain this cluster and close it out,” Hendy said.

He cautioned that this did not mean the danger was gone, however, as the huge Sydney outbreak had also been conclusively linked to its source early on.

That person arrived on August 7 – meaning it was unlikely the disease had been spreading for weeks, as was earlier feared.

“In Sydney they did have that link early on, and they were not aggressive enough. We still have to be quite aggressive,” Hendy said.

His modelling suggested there were likely about 100 cases as of Wednesday, when the country went into lockdown.

But the lockdown should see the rate of transmission dropped by about 80 per cent, he said, bringing the overall transmission rate to about 0.5. This would mean that eventually under level 4 the virus would die out, as on average only half of those infected would pass it on to another person.

Given how early it was in the cluster, Hendy suspected the Government would extend the level 4 settings nationwide, at least across the weekend, when the costs of lockdown are lower.

University of Otago epidemiologist Michael Baker agreed, saying the level 4 settings made contact tracing far easier given everyone in the country was already being told to self-isolate.

“Already they are doing what the contact tracers would ask them to do: Which is staying put,” Baker said.

He said local lockdowns were very hard to properly police and the possible presence of Covid-19 in a holiday hotspot like Coromandel meant it could easily have travelled around the country.

“It's nice in theory, the geographically focused lockdown, but the reality is it’s hard to deliver it.”

No wastewater testing outside of Auckland has shown positive results, with recent negative results for Wellington, Nelson, Christchurch, Queenstown and Invercargill.

Health director general Dr Ashley Bloomfield said he would want to see around one per cent of all the population tested in other areas to make sure Covid-19 was not loose, but in recent weeks less than one-in-10 people with cold-like symptoms had got tested.

“If you look at through winter, we were probably getting somewhere between five and 10 per cent of symptomatic people routinely being tested. We want to get that much closer to 100 per cent.”