Simon Bridges on his demotion after alleged comments to Jacqui Dean

National MP Simon Bridges has hit back at his demotion by leader Judith Collins last night, calling it "truly desperate".

Bridges spoke outside Parliament less than 12 hours after his demotion over alleged comments to fellow National MP Jacqui Dean.

Bridges said it showed Collins will go to any length to hold on to the leadership.

He said there was a huge amount he wanted to say about what happened yesterday and how wrong it was and he would after talking to the caucus first.

He had clear views about what he thought should happen to the National Party. He planned to hold a full press conference as soon as possible after that. Caucus was meeting at 9am.

He sought a caucus meeting yesterday, but said Collins refused even though she was still at the precinct.

She had finally agreed to having one this morning and he was looking forward to it.

He will hold a fuller press conference after speaking to caucus. The Herald understands he has no intention of resigning.

National MP Jacqui Dean. Photo / file

Collins announced Bridges' demotion in a release just after 9pm on Wednesday.

The MP who laid the complaint against Simon Bridges is understood to be Jacqui Dean. It is understood to relate to crude comments Bridges allegedly made at a function about five years ago.

Bridges is understood to have been talking with a group of about three fellow MPs, including Jami-Lee Ross and Todd McClay, when Dean walked past and the Tauranga MP called to her and made the comment.

'National Party will not tolerate harassment and intimidation'

In a written statement last night Collins said: "This evening, with unanimous support of the board of the National Party, Simon Bridges, Member for Tauranga, has been demoted and relieved of his portfolio responsibilities.

"The decision follows an allegation of serious misconduct relating to Simon Bridges' interaction with a caucus colleague."

It comes as speculation rises that Bridges was preparing to roll Collins as leader of the party.

It is understood Bridges and the National MPs who back him tried to call a caucus meeting on Wednesday night but Collins blocked it.

Some MPs are furious at Collins' move, saying it was a "ugly" and "f***ing ridiculous", and a clear bid to halt any leadership bid by Bridges by dredging up remarks from five years ago.

National leader Judith Collins demoted former leader Simon Bridges last night. Photo / Mark Mitchell

The written statement from Collins said the incident related to comments made by Bridges to a female caucus colleague at a function a number of years ago.

"Having been made aware of the seriousness of the complaint for the first time and the ongoing distress this has caused the complainant, I was left with no option but to immediately demote Simon Bridges and relieve him of his portfolio responsibilities," Collins said.

"This decision has not been made lightly. However, the seriousness of the situation demands a swift and decisive response.

"Under my leadership, the National Party will not tolerate harassment and intimidation of any person.

"Members of Parliament and staff should be able to conduct their duties at all times without feeling unsafe or intimidated, and all deserve to be treated with absolute respect by their colleagues in all situations."

Other caucus colleagues reacted with surprise, when approached by the Herald. One said it was a "complete stitch-up" of Bridges by Collins.

National MPs were already expected to likely have an awkward caucus meeting today after a poll showing Collins had lost the support of both National voters and the country at large.

A Newshub-Reid Research poll asked whether Kiwi voters preferred Bridges or Collins to lead the National Party.

Bridges was backed by 40.7 per cent of voters, with Collins having the support of just 23.3 per cent - the remainder didn't know.