As New Zealand marked 100 days without community transmission of Covid-19, National Party deputy leader Gerry Brownlee says the Government's warning of an approaching second wave is "very puzzling".

The Ministry of Health announced the milestone on Sunday, with no further new cases in of the deadly virus reported for the fourth consecutive day.

There remain 23 active cases of coronavirus nationally, all in managed isolation facilities, while the number of New Zealand's confirmed cases remains at 1219.

Director general of health Dr Ashley Bloomfield thanked every person who had been tested for Covid-19, saying Sunday marked a "significant milestone".

"However, as we all know, we can't afford to be complacent," he said in a statement.

"We have seen overseas how quickly the virus can re-emerge and spread in places where it was previously under control, and we need to be prepared to quickly stamp out any future cases in New Zealand. Every person in the team of five million has a role to play in this."

But Brownlee told Newstalk ZB the Government's warning of an imminent second wave of Covid-19 in New Zealand was "puzzling".

"People have made a big effort on this and they expect to get all the relative freedom," he said.

"None of us are complacent about it, I believe, it is something that is going to be with the world from this point on."

In recent days Bloomfield urged Kiwis to "be ready" and have a stock of masks on hand in household emergency kits should we see an outbreak similar to the one sweeping through Victoria.

Health Minister Chris Hipkins last week announced Kiwis would be encouraged to wear masks in public places if New Zealand moved back to level 2, and encouraged them to prepare some in the meantime.

And public health expert Michael Baker suggested a mask day – in which New Zealanders all wear masks to work, as a trial run for a time when Covid might return.

The advice comes after months of officials saying there was not yet enough evidence that mask use protected the public from Covid-19.

Hipkins said the evidence had changed, and that "we are now in a different situation to where we were previously".

After renewed warnings from Bloomfield in the last week about a potential outbreak, Brownlee called on the Government to "come clean" on the rate of Covid-19 infections in New Zealand.

"We have had three months of no community transmission, then inexplicably, the director-general of health Ashley Bloomfield tells the nation that a second wave was a likely prospect," he said in a statement.

"It doesn't add up. Why announce this now when there are few cases?"

But surges of Covid-19 have been seen recently in Victoria, Hong Kong and Vietnam - all regions which had previously kept the virus contained.

On Sunday Victoria recorded the highest number of people to die in a single day in Australia since the pandemic began - 17 people, with another 394 infections announced.

Of the new cases announced, 43 people were in intensive care, and 26 were on ventilators.

Meanwhile on the heels of the National Party's list release, Brownlee said he believed National MP Alfred Ngaro could beat Labour's Phil Twyford to return to Parliament.

Ngaro, who dropped 10 places on the list to Number 30, will almost certainly have to oust Twyford in Te Atatu to return.

"I think he can win that seat," he told Newstalk ZB.

"You're up against Phil Twyford, who, despite being the architect of much of the non-delivered policies from Labour – KiwiBuild and light rail, etc - is number four, so he's going to be in Parliament anyway."

He is also confident that Christoper Luxon, who is at number 61, can win his seat of Botany.