Prime Minister Jacinda Ardern has taken aim at the National Party for pedalling "nonsense" rhetoric the Government knew about the Covid-19 cases long before telling the public.

National's deputy leader Gerry Brownlee says he thinks it's "interesting" Kiwis were warned there could be another outbreak about 10 days ago and told to stock-up on masks.

"And then you had the Prime Minister's visit to the mask factory [on Tuesday] ... all very interesting things to have happened a matter of hours before a large residential area of New Zealand went into level 3 lockdown," said Brownlee.

"I'm just outlining facts. It's an interesting series of facts."

Brownlee last week asked: "What do these guys know that they are not telling us?"

Ardern said Brownlee's idea the Government was holding back critical information was "just nonsense".

"There is no reason why we would ever do that. I hope that from the timeline we have set out, we have been very, very quick - including informing the public.

"I do worry that those kinds of theories do nothing to support what needs to be collective action from all of us."

At both last night's and this morning's press conferences, Ardern said the first she knew about the confirmed case was about 4pm after a public event in Whanganui - which was at a mask factory.

When Ardern got back to Wellington she met with All Of Government officials about 7pm then consulted the Ministers with Power to Act - a small group including the Health Minister, Finance Minister and the Deputy Prime Minister.

She then briefed National leader Judith Collins and Auckland Mayor Phil Goff before holding the 9.15pm press conference.

Bloomfield said he was first told about 2.40pm via a text from the head of the Counties Manukau District Health Board.

Ardern said there were no delays in taking action.

"As soon as the person tested positive at 2.30pm, they went into isolation. The idea that something only happens once we inform the public is incorrect.

"As soon as that result is received, that person goes into isolation, everyone around them goes into isolation, contact tracing starts straight away. The gears do not start turning once we tell the public - that happens well before."

Deputy Prime Minister Winston this afternoon took aim at Collins for blaming the Government for the new cases.

"That's haphazard and careless and irresponsible and not befitting of someone with legal training and some experience in the law. You get the facts right before you make claims like that."

Act leader David Seymour also distanced himself from the theory the Government knew more than it was letting on, saying he took Ardern at her word.

"I don't think there's any evidence they knew otherwise. I think we do actually have to take people at their word. We expect the Government to be to be open and transparent.

But he caveated it by saying "if it was ever found she'd lied about that I think she'd have to resign" and said it would be a "bigger scandal than Erebus".