Mark Mitchell calls Judith Collins' Simon Bridges announcement 'deeply disrespectful', confirms caucus meeting, won't rule out leadership challenge

National MP Mark Mitchell has labelled leader Judith Collins "deeply disrespectful" for announcing Simon Bridges' demotion without briefing caucus, and won't rule out a leadership challenge being mounted on Thursday.

In a bombshell statement late on Wednesday, Collins said Bridges, the former leader, had been demoted and relieved of his portfolio responsibilities following an "allegation of serious misconduct" towards a caucus colleague a number of years ago.

Newshub understands the complaint relates to something that happened five years ago. A group of National MPs including Bridges, Jami-Lee Ross and Todd McClay were together with Waitaki MP Jacqui Dean. The allegation is that something was said to her of a sexual nature that Dean found humiliating and designed to dominate. The complaint was taken to then-leader Bill English, who has refused to comment to Newshub.

It's been widely speculated in recent weeks Bridges wants to challenge Collins for the leadership, with the Tauranga MP not ruling it out to Newshub this week, simply saying it was "not my intention" to do so.

Supporters of Bridges have told Newshub Wednesday night's development was a set-up.

Speaking to Newshub political editor Tova O'Brien late on Wednesday, Mitchell said caucus would come together on Thursday - the first time the MPs had met on the issue.

"There has not been any caucus meeting yet. It is really important that happens. Once we have come together tomorrow, we will be able to come out and give you a much clearer picture of what is going on," the MP said.

Asked if there would be a leadership challenge, Mitchell would not rule it out. 

"I am not going to discuss that now. I need to respect my caucus colleagues. We need to get together tomorrow to discuss what has unfolded. I don't know what is going to unfold tomorrow. There has obviously been a big announcement today."

He said a leadership challenge was not on the agenda for Thursday and wouldn't say if Bridges had the numbers.

But he admitted both Bridges and the caucus had been "blindsided" by Collins' statement.

"Completely flying blind. No one has actually spoken to caucus and briefed us and talked us through it."

Mitchell was asked by O'Brien for his thoughts on Collins' behaviour.

"In my view, it was deeply disrespectful to the caucus and the caucus, we should have been brought together and it should have been discussed, and I am sure that will be one of the issues that will be raised tomorrow when the caucus meets."

He said he was not aware about the details of the allegations or what was allegedly said by Bridges.

"Tomorrow is an opportunity for us as a caucus to find out exactly the substance of these allegations. Until we have met as a caucus and we actually know. We have no idea what the allegations are. The press statement said they were serious so let's get together in caucus and find out exactly what they are."

The development was "not good" for the National Party, but he didn't believe the party's future was at stake and felt its brand was still "very strong".

"It is not good. But we have to address that and we have to talk about that tomorrow. It is time for us to step up and start being the Opposition this country deserves."

Mitchell expects party president Peter Goodfellow will brief MPs on Thursday. While Collins said on Wednesday that the board unanimously agreed to Bridges' demotion, National Party sources have told Newshub there was no vote.

Newshub attempted to speak to other National MPs outside Parliament late on Wednesday. Most - including Melissa Lee, Michael Woodhouse, Matt Doocey, and Maureen Pugh - refused to comment.

Chris Penk said he wanted to hear from all sides before passing judgement.

"I'm not going to comment on stuff until we've had a chance to hear from all sides and that's really important. Natural justice has a place in the way we conduct business.

"It's important that we have these discussions in a way that allows everyone to have their say and I'm not convinced that's happened so far."