Key points:

Joyce confirms ex-staffer Vikki Campion is now "partner" but denies breaching ministerial rules

Apologises to estranged wife, children and Ms Campion for "all the hurt"

Denies reports of misconduct at 2011 event and has sought legal advice

AAP understands a group of about four or five Nationals MPs are trying to get Mr Joyce to resign as pressure mounts over his affair with former staffer Vikki Campion, but they don't have the numbers in the 21-member party room to force a change.

Veterans Affairs Minister Michael McCormack, who missed out twice on becoming deputy leader, on Tuesday night denied he had been having conversations with colleagues to replace Mr Joyce.

"No I haven't," he told reporters in Canberra on Tuesday.

It comes after former deputy prime minister and Nationals leader Warren Truss said on ABC's 7:30 program on Tuesday that Mr Joyce's leadership was "diminished".

While expressing continued support for Mr Joyce, Mr Truss said that "he needs to demonstrate that he's got the capacity to continue to do the job".

"National Party members … would be remiss in their duties to their electorate if they weren't seeking to resolve this issue constructively and quickly."

Prime Minister Malcolm Turnbull reaffirmed that he continued to have confidence in Mr Joyce as the Nationals leader faces questions over the appointment of his lover to government jobs last year.

Asked by Labor leader Bill Shorten on Tuesday whether he retained confidence in Mr Joyce, Mr Turnbull said: "Yes."

Answering a second question, Mr Turnbull said all ministers were bound by the standards code and Mr Joyce had explained his circumstances in a statement.

"The facts of the relationship which you're referring to are of course known to the deputy prime minister.

Related reading Barnaby Joyce and Vikki Campion relationship timeline

"It is his responsibility to address it and comply with the standards. And he's answered that, he's addressed that in his statement today."

Resources Minister Matt Canavan, who was one of the National MPs who hired Vikki Campion, told parliament the job was organised in consultations between his office and the deputy prime minister's office.

"I had no knowledge of the relationship between Mr Joyce and Ms Campion at the time," said Senator Canavan - who was Mr Joyce's chief of staff before entering parliament.

"And as he (Mr Joyce) has said in his statement this morning, she was not his partner at the time."

Mr Joyce denied breaching ministerial rules over his affair with a former staffer and threatened legal action against one of his "bitterest political enemies" for spreading allegations about sexual misconduct at an event in 2011.

The defiant Nationals leader gave a brief statement to the media ouside Parliament House on Tuesday morning. He did not take any questions but gave no indication he was considering resigning over the growing scandal.

Mr Joyce apologised to his estranged wife and his daughters "for all the hurt" caused by the fallout from his recently exposed affair with his former media advisor Vikki Campion, who is now pregnant with their child.

He also apologised to Ms Campion, whom he conceded was now his "partner".

"To Vikki Campion, how deeply sorry I am that she has been dragged into this," he said.

No breach of ministerial rules: Joyce

The ministerial code of conduct says partners and close relatives of ministers are not allowed to be given jobs within the minister's office, or with other members of the executive, without the express permission of the prime minister.

Ms Campion was moved from Mr Joyce's office into the employment of Nationals colleague Matt Canavan, and then to the office of Damien Drum.

Malcolm Turnbull's office said the prime minister had never needed to grant permission because Ms Campion was not Mr Joyce's "partner" at the time.

Speaking with reporters on Tuesday morning, Mr Joyce denied breaching the code.

"It is without a shadow of a doubt that Vikki Campion is my partner now," Mr Joyce said.

"But when she worked in my office, she was not my partner. When she worked in Matt Canavan's office, she was not my partner. And Damian Drum was not a minister."

Reports of 2011 incident 'untrue'

Overnight the Daily Telegraph and Courier Mail reported on an incident in 2011, separate to the affair with Ms Campion, alleging inappropriate behaviour.

Mr Joyce strongly denied the report and said he would consider legal action, claiming the story was "peddled" by one of his "deepest political enemies".

"It's not a case that I didn't recollect it. It did not happen," Mr Joyce told reporters.

The deputy prime minister said he had already engaged lawyers and was considering action.

"I have consulted senior legal advisers and reserve the right to take action for what is serious defamation," Mr Joyce said in a written statement.

Labor says Joyce's leadership becoming 'untenable'

The public defence comes amid reports of unnamed Coalition members expressing doubt in Mr Joyce’s leadership credentials, especially when he is due to serve as acting prime minister while Malcolm Turnbull is in the United States next week.

Coalition senator Ian Macdonald was asked if Barnaby Joyce should step down.

"I'm sure he is considering all his options," he told reporters on Tuesday morning.

Finance minister Mathias Cormann said the leadership of the Nationals party was a "matter for the Nationals".

"We all support Barnaby as a valued friend and colleague," Mr Cormann said.

Speaking before Mr Joyce's public denial, Labor MP Chris Bowen said the alleged 2011 incident was "very serious" and required a full explanation.

"Barnaby Joyce's position is becoming increasingly untenable," Mr Bowen said.

The Australians Greens say Mr Joyce should resign his frontbench role and the Nationals leadership.

The Greens party room unanimously resolved the position at a meeting in Canberra on Tuesday.

Barnaby Joyce and Vikki Campion timeline

2016

May - Vikki Campion assists Barnaby Joyce's election campaign as media adviser, having previously worked with NSW government ministers and News Corp

August - Campion joins Joyce's staff. She splits with fiance John Bergin, three months before they were due to wed. Friendship develops between Joyce and Campion

December - Chief of staff Di Hallam reportedly seeks Joyce's approval to have Campion transferred out of office. Hallam later quits to take up departmental role

2017

February - Campion is photographed in a Sydney bar with Joyce

April - Barnaby's wife Natalie reportedly confronts Campion in Tamworth. Campion goes to minister Matt Canavan office as adviser. Natalie and Barnaby seek to make marriage work

May - At NSW Nationals conference in Broken Hill colleagues describe Joyce as "a mess"

June - Natalie and Barnaby show up together at Canberra press gallery midwinter ball

July - Campion leaves Canavan office after he quits frontbench over citizenship. She temporarily goes back to Joyce's office

August - Campion moves to Damian Drum's office in a social media adviser position specially created for her. He already has a media adviser. Prime Minister Malcolm Turnbull is reportedly reassured by Joyce the relationship with Campion is over. Drum says he was told the same thing. Former Joyce chief of staff Di Hallam takes up a senior position with the Inland Rail project

September - Natalie reportedly asks family friend, Catholic priest Father Frank Brennan, to counsel Joyce. Campion is seen managing Joyce media events at federal Nationals conference in Canberra

October - Campion reportedly takes stress leave. Writ issued for New England by-election after Joyce quits over dual citizenship

November - Natalie holidays in Bali with a daughter. Man in a pub in Inverell angers Joyce during election campaign by reportedly saying: "Say hello to your mistress"

December - Joyce wins by-election. Joyce tells parliament during same-sex marriage debate he is separated. Campion's redundancy package is approved. They move into an Armidale property provided rent-free by businessman Greg Maguire

2018

January - Joyce and Campion holiday in north Queensland and NSW north coast

February - Joyce tells reporters Campion is now his partner. But denies she was his partner when she worked in Canavan's office

Mid-April - Joyce-Campion baby is due

(Source: Based on media reports and official statements.)

- with AAP