A disease modelling expert is warning the latest COVID-19 outbreak is likely to grow bigger than the one in August 2020 and could reach as high as 1,000 community cases.
New Zealand recorded 35 new community cases on Monday - the highest number recorded so far - bringing the total number of cases in the community outbreak to 107.
Professor Shaun Hendy, a COVID-19 modeller at the University of Auckland, told Newshub on Monday it was "slightly unwelcome news".
"I'd rather have seen something closer to what we saw yesterday," he said.
When Case A was detected last Tuesday early modelling predicted 50 to 120 cases in the community at the time of detection.
Most of the cases reported this week would have been infected prior to lockdown.
Hendy hopes cases will peak by the middle of the week as we should begin to see the effect of the lockdown on case numbers.
"We hope so, I mean it might be a very slight decline but we'd like by the end of the week to see smaller numbers, that would be the best case."
However, he warns the outbreak will continue to grow.
"I would say a best case scenario would be something like what we saw in August last year - probably, higher than that. Maybe 200 [cases] might be the best case scenario but it could go as high as 1000 [cases]. That's still a possibility.
"But we will see later this week how alert level four is working and it's alert level four which will actually determine the number of cases in this cluster."
He said the most important thing for upcoming predictions is looking at the effectiveness of the COVID-19 lockdown on curtailing the spread of the virus.
"At the moment we don't know how level four has been working for the Delta variant," Hendy said.
"It's the first time an outbreak of the Delta variant in NZ so we don't have much information on that."
Prime Minister Jacinda Ardern confirmed New Zealand's alert level four lockdown will be extended for at least another four days, and Auckland will continue until at least next Tuesday.
Ardern said Delta "had a head start on us", and points to the transmission rate and how it's spreading so fast.
"We have some way to go yet."
Ardern said the extra four days will give them additional data, testing across known contacts, and "a level of reassurance".