The men hoping to take Jacinda Ardern’s role as PM

Jacinda Ardern's opponent at September's election will become known on Friday, when New Zealand's National party holds a leadership ballot between incumbent Simon Bridges and challenger Todd Muller.

Momentum is growing behind Mr Muller, the party's agriculture spokesperson, who has rallied support in the wake of a poll published by Newshub on Monday.

National was the first-choice party of just 31 per cent of Kiwis, down from 44 per cent at the 2017 election and at the last poll, taken in February.

A second poll on Thursday night by 1News confirmed the malaise, with National slumping to just 29 per cent.

New Zealand's Prime Minister Jacinda Ardern
Jacinda Ardern's opponent at September's election will become known on Friday. Source: AAP

On those numbers, Ms Ardern's Labour would govern without the need for current coalition partners NZ First or the Greens, and National would lose more than a quarter of their caucus.

Both pollsters last surveyed New Zealanders in February; both had National ahead of Ms Ardern's Labour.

In between came COVID-19, which flipped the political dynamic and put Ms Ardern in control just four months from the election.

Even more devastating for Mr Bridges was a word cloud, reported by Newshub, where the most common word associated with the 43-year-old was “idiot”, followed by “don't know” and “average”.

Responding to Thursday's poll, Mr Bridges said he wouldn't resign ahead of Friday's spill.

"If you look at this poll, it's COVID-19," Mr Bridges told 1News.

"I'm very confident (of winning) but these are now matters for the caucus."

National is a conservative party in politics and nature; supporters from either camp weren't willing to speak publicly to AAP.

But Mr Muller's impressive CV gives some in the National party room hope the 51-year-old could inspire a revival of electoral fortunes.

Todd Muller (L) and Simon Bridges (R). Source: Twitter/AAP
Todd Muller (L) is challenging Simon Bridges (R) for the National Party leadership. Source: Twitter/AAP

As a staffer to former prime minister Jim Bolger, he turned down the chance to enter parliament in his 30s and instead worked in two iconic New Zealand industries; kiwifruit and dairy, with giant Fonterra.

Fonterra chief executive Miles Hurrell declined to endorse Mr Muller in an earnings briefing on Thursday, saying "we don't make any comments on what happens in Wellington".

Another industry insider spoke on condition of anonymity.

"He was a chief executive of (kiwi fruit and avocado packing company) Apata, he led a 400-strong blue collar workforce with a $NZ50 million turnover," they said.

"At Fonterra he emerged as a leader ... I remember people saying 'who's Todd Muller?'

"He had an ability to bring together board directors, the farmer co-op shareholders, iwi (Maori leaders), community leaders and get along well with all of them."

After that success, Mr Muller entered parliament in 2014.

In Wellington, his stand-out achievement to date was as climate change spokesperson, handling negotiations to a point where National - with a diversity of views on climate science - supported the government's Zero Carbon Bill.

"In this moment of economic crisis, we need someone with depth of business experience and networks and an understanding on how to get the best out of a team," one MP told AAP.

"Todd is proven on all those levels.

"There's a strong mandate for change and there's a lot of people in the National party who strongly believe Todd has what it takes to be a great National prime minister."

Whether Mr Muller gets that chance will depend on Friday's vote of 55 National MPs

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