UPDATE:  NATIONALS leader and Deputy Prime Minister Barnaby Joyce has sensationally stepped down after a tumultuous period in the public eye. 

He announced he will resign to the party room on Monday morning after a formal complaint of sexual harassment was received by the Nationals Party.  Mr Joyce has denied the allegations and urged they be investigated. 

His affair with now-pregnant staffer Vikki Campion prompted a swell of public backlash this month. 

EARLIER: AFTER a tumultuous month for the Deputy Prime Minister, Barnaby Joyce is tipped to step down as Nationals leader in an imminent press conference.

The announcement in Armidale is expected at 2pm (AEDT) and several publications are suggesting the scandal-struck politician could announce his resignation.

Pressure has been mounting on Mr Joyce ever since it was revealed that he had an affair with his staffer Vikki Campion, who is now his partner.

It went from bad to worse for Mr Joyce this week. Yesterday, he denied claims of sexual harassment against him as "spurious and defamatory" as he faces fresh questions about an 11-day road trip he undertook in December.

Just hours ago, Nine News political reporter Lane Calcutt asked the Deputy PM if he was going anywhere following the sexual harassment complaint.

"Let's just do the presser," he said.

The press conference is expected at 2pm (AEST). Picture: Hollie Adams/The Australian. Source: News Corp Australia.
The press conference is expected at 2pm (AEST). Picture: Hollie Adams/The Australian. Source: News Corp Australia.

A spokesman for Mr Joyce told The Daily Telegraph he had been made "indirectly aware" of the claim which he described as "spurious and defamatory".

"He said allegations of wrongdoing should be immediately referred to police so that the veracity of any claim could be properly tested," the spokesman said.

Now, Mr Joyce faces a formal leadership challenge with a possible showdown next Monday after a Nationals MP announced he would move a resolution ousting Mr Joyce as party leader.

The warning from Andrew Broad, member for the Victorian seat of Mallee, is the first public sign of a move against Mr Joyce since his affair with a staffer was revealed.

Earlier today speaking from Washington, Prime Minister Malcolm Turnbull dodged questions about whether he wanted Mr Joyce to remain as the Nationals leader.

"Barnaby Joyce is the leader of the National Party of Australia. As leader of the National Party of Australia in a Coalition government, he is my Deputy Prime Minister," Mr Turnbull said.