Mr Bridges has faced white-hot pressure to keep his job since the release of a horror poll on Monday showing his National party had just 31 per cent support and faced another term in opposition.

That's down 13 points from both the last poll and the party's 2017 election result, when National finished eight points above Jacinda Ardern's Labour but was unable to form a coalition.

While Ms Ardern has been credited with an adept and pitch-perfect response to the coronavirus crisis, Mr Bridges has drifted from political relevance.

Murmurings of discontent have been evident for some time, with senior MPs declaring 35 per cent would be a pass mark for their embattled leader.

The 31-point result brought dissatisfaction to the surface, but it was Mr Bridges himself on Wednesday who confirmed the leadership challenge.

"A couple of my colleagues want to challenge myself and Paula Bennett for the leadership and deputy leadership," he said.

"We need to resolve this quickly so we can get back to focusing on what matters."

On Wednesday afternoon, Mr Muller outed himself as the contender in an email to all 55 National MPs laying the basis for his leadership.

"This country faces the most enormous challenge since the end of the Second World War. Labour has failed to deliver on every measure it has set for itself in government," Mr Muller writes.

"Our communities and our economy are at stake. 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."

Mr Muller, 51, is a low-profile ex-staffer to former Prime Minister Jim Bolger, who spent more than a decade in agri-business before entering parliament in 2014.

Running on his ticket as deputy is Nikki Kaye, the more liberal Auckland Central MP, best known for twice beating Ms Ardern to that seat.

The challenge was to be heard on Tuesday but in a bold power-play, Mr Bridges called an emergency meeting for Friday, giving Mr Muller less time to manouevre.

"I'm very confident ... Paula and I will win. We're putting it to the test to resolve it quickly," he said.

"I think the overwhelming majority of the caucus are behind me."

Two-time leadership aspirant Judith Collins ruled herself out of the contest and called on her party to solve the leadership question quickly.

"Disunity is terrible in terms of the people and the polls ... they need to sort it out as fast as possible," she said.

Mr Bridges' move to bring the ballot forward carries risk.

While the Newshub-Reid Research poll was destructive, a second poll to be announced by 1News-Colmar Brunton on Thursday will still be ringing in the ears of members as they vote.

Australian Associated Press