National MPs will hold an emergency caucus meeting at midday on Friday as Simon Bridges seeks to stare down a prospective leadership challenge.

Bridges said this morning that he was being challenged for the leadership after the Herald reported yesterday that a no-confidence vote would be mounted against him at the party's next regular caucus meeting on Tuesday.

The caucus will now meet on Friday as Bridges seeks to front-foot a challenge, reducing the time challengers would have to lobby MPs for change.

Bridges was referring to MP Todd Muller and Nikki Kaye, who would likely stand as Muller's deputy leader.

As yet, there has been no comment from Muller or Kaye, but other MPs are now starting to talk about the issue.

Prime Minister Jacinda Ardern declined to comment on the apparent coup attempt.

She said her focus was on running the Government and, given her experience in opposition, it was her policy to not comment on a rival party.

"I'm focused on jobs and employment," she told reporters this afternoon.

• National MP Judith Collins believes no-confidence vote will fail

Speculation is rife that Todd Muller will challenge Simon Bridges for the National Party leadership.

National MP Sarah Dowie, who will not be standing for re-election at September's election, said she supported Bridges and the leadership challenge was a distraction for the party.

"This is typically not the way we behave."

Dowie said Bridges did the right thing by throwing down the gauntlet to any MPs looking to challenge him for the leadership to come forward.

"If they have an issue with leadership, they need to be upfront, or speak up in caucus."

Brett Hudson was also in support of Bridges, who he said was the "right leader for National at this time".

National should be focused on New Zealand, and New Zealanders at this time, he said.

"I can't think there would be a single New Zealander that thinks we should be focused on ourselves rather than them."

Hamilton West MP Tim Macindoe said he would not throw his support behind anyone until he knows there will for sure be a challenge.

"You wouldn't bet on a house without knowing the other horses in the field," he said.

If there was a challenge, Macindoe would be voting for someone who was going to present the "best option for a strong National campaign".

National MP for Helensville Chris Penk said he'd back the party's current leadership team "in pretty clear terms" and didn't think the time was right for a leadership challenge.

"There's a few names swirling around but for me it's that we've got to be talking about the things that matter. A lot of New Zealanders are hurting right now."

Judith Collins has ruled out challenging Bridges, and said she has no intention of contesting the leadership. Mark Mitchell has also said he is backing Bridges and will not challenge him.

However, Mitchell could contest it if the position was open.