There are calls for masks on public transport to be reinstated following a jump in COVID-19 cases in the past week.
A total of 20,522 new cases over the past week were reported on Monday - over 4000 more than the previous week.
But modellers said the real number of cases could be double that because people are slacking off on reporting and testing when symptomatic.
"We're seeing a real increase in cases, pretty much since the middle of September, and that's ongoing," said COVID-19 modeller David Welch.
He also believes many people aren't testing when they're symptomatic and the true number of cases could be much higher.
"Forty or 50,000 a week I'd say is probably the number of actual infections out there," he said.
It's not one variant driving it - there are various Omicron subvariants circulating. And as cases rise, some experts are calling for the return of certain restrictions, like masks on public transport.
"Many commuters are spending hours every week jammed into an environment that we know has very poor ventilation," said epidemiologist Professor Michael Baker.
"When we made those decisions around our health measures, we did so knowing there would likely be an increase prior to Christmas - and that is what we are seeing," said Prime Minister Jacinda Ardern.
Prof Baker also wants the Government to better communicate the risk of COVID-19 infections, especially as cases climb.
"We need a very clear statement about the level of risk that everyone understands, and what to do at different levels of risk," he said.
Ardern said the Government continues to take COVID-19 seriously and she believes the public does too.
But it appears they may not be taking it seriously enough. More than 1.5 million Kiwis eligible for the booster jab are yet to get it.
"I would strongly encourage them to get that. That's the main thing keeping people out of hospital at the moment," Welch said.
Only about 10 percent of new cases are COVID-19 reinfections, so the virus appears to be seeking out those who've escaped it so far, especially older people who aren't as vigilant as they were earlier on in the pandemic.
"They are possibly relaxing their guard a bit, getting out more, which is understandable, and getting the virus," Prof Baker said.
