Todd Muller confirms leadership challenge, tells National MPs Simon Bridges cannot win election

National MP Todd Muller has confirmed his formal leadership challenge against incumbent Simon Bridges in an email to his colleagues on Wednesday.

In the email, which was seen by Newshub, Muller says National cannot win the election under Bridges. He also said he had formally notified his leader and National Party president Peter Goodfellow of the challenge.

"It is essential that National wins this election," the Bay of Plenty MP wrote. "I share the view of the majority of my colleagues that this is not possible under the current leadership."

The challenge followed a Newshub-Reid Research poll showing National down to 30.6 percent and Bridges' preferred Prime Minister ranking down to 4.5 percent. 

Bridges confirmed to The AM Show on Wednesday morning that two MPs are challenging National's leadership - but wouldn't say who. 

"I think it's for them to make clear their leadership intentions and I want to just give them the dignity of being able to do that and choose how they do."

He said he was "very confident" that he will win the challenge "but obviously we're putting that to the test so we can move on from the distraction really quickly and get back to what matters".

Muller's Bay of Plenty electorate neighbours Bridges' Tauranga electorate, and their constituents echoing what Newshub's latest poll showed: the country doesn't like Bridges.

Almost everyone Newshub spoke to preferred Muller.

One person described Muller as "the man for the moment", while another person said he seems like "quite a fair sort of guy to talk to".

"I think if they're to have any chance at all it's really got to be Muller," Newshub was told, as another said it's "probably time for a change - maybe Todd".

But Bridges has some surprising support from former coup challenger-in-chief Judith Collins.

Newshub asked the National MP if she wants to be leader, and she said: "No, it's a tough job."

Collins said she thinks Bridges will survive the leadership challenge, but she would not comment on Todd Muller as leader or his potential ticket with Nikki Kaye.

"You'll have to talk to them.... Look, everyone talks about things but I'm not going to answer for them."

Muller wasn't at his electorate office on Wednesday, and Newshub understands that's because he's been holed up at the Cordis Hotel in Auckland, meeting with MPs.

Kaye wasn't home either. The Auckland Central MP has something going for her - she's taken Jacinda Ardern on twice in Auckland Central and won.

The Prime Minister wouldn't be drawn into the controversy when asked about it on Wednesday.

"For the fact I have had my own experiences in Opposition is probably the reason that actually I have a policy of just not engaging in other people's politics - it's a matter for them."

Muller said in the email that New Zealand faced its biggest challenge since World War II and that National needs to regain power to steer the country through the crisis.

He said Labour's re-election would be "catastrophic for two generations".

Analysis by Political Editor Tova O'Brien

Both camps are confident. Team Bridges is predicting a win, and Team Muller says the numbers are very strong for their guy.

And Muller has put it in writing, sending an email to colleagues Wednesday afternoon saying he notified Simon Bridges and the party president that he would be seeking a ballot for the leadership of the New Zealand National Party as soon as is convenient for the caucus.

He says it is essential National wins this election.

"I share the view of a majority of colleagues that this is not possible under the current leadership... I believe I am best placed to earn the trust of New Zealanders by September 19."

Newshub understands Nikki Kaye is Muller's preference for deputy.

We'll find out how it shakes down at coup o'clock - just two sleeps.

MPs have been summoned back to Parliament for an emergency coup caucus on midday Friday.

Brace yourselves for knives at noon.