Mr Johnsen was suspended from the National party last week over allegations he raped the woman at a Blue Mountains lookout in 2019.

He strenuously denies that allegation and has not responded to requests for comment on new allegations raised on Tuesday morning that he sent lewd messages to the woman during question time and a video of himself masturbating in a toilet.

He will remain in Parliament as an independent until he resigns or is expelled by his colleagues, a step not taken in the Legislative Assembly for more than 100 years.

Premier Gladys Berejiklian, Deputy Premier John Barilaro and opposition leader Jodi McKay all called on Mr Johnsen to quit.

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Transport Minister Andrew Constance said Mr Johnsen had to "go today" and the people of NSW "don't deserve this guy in Parliament".

Mr Barilaro, the Nationals leader, sent text messages to Mr Johnsen in the morning seeking his resignation, but these had gone unanswered by 6pm.

Mr Barilaro apologised to the "citizens of the Upper Hunter" for "what has happened".

He conceded the Coalition could lose the seat to Labor if a by-election were held, cementing the government's minority status.

"But I'd rather stand here doing the right thing than worrying about a majority in government," he said.

He said he was "confident" Mr Johnsen would decide that the "best course of action" was to step down, but that had not happened by Tuesday evening.

If he did not resign, Mr Barilaro said the government would examine whether to expel him when Parliament resumed in May.

Labor has been debating behind the scenes whether to try to expel him sooner.

Ms McKay said in a radio interview that, if Mr Johnsen were a member of her party, she would seek to recall Parliament immediately and vote on expelling him.

Police are investigating an allegation made public last week that Mr Johnsen raped the woman during one of their sexual encounters in September 2019.

Labor MP Trish Doyle told Parliament last Wednesday that the woman alleged she had met a government MP for paid oral sex at a Blue Mountains lookout but "towards the end the man moved around behind her and assaulted her in a way she had not consented to".

Mr Johnsen outed himself as the subject of the allegations and police confirmed they were investigating the matter. He was due to talk to police on Friday, but the interview was postponed.

The new sexting allegations were detailed in an ABC report on Tuesday morning. The ABC said it had seen text messages between Mr Johnsen and the sex worker, one of which included a video of a man masturbating.

Mr Barilaro said on Tuesday that he had told Mr Johnsen that "outside of the [rape] allegations" his behaviour as a parliamentarian was unacceptable.

"The text messages are there for everybody to read," he said.

"I contacted Mr Johnsen to express the view that his position as a member of Parliament is untenable."

Ms McKay, recounting the ABC allegations, told a media conference on Tuesday that Mr Johnsen had been sexting the woman while sitting in the chamber during a debate over water restrictions at a time when drought-affected towns in his electorate had run out of water.

"It's September 2019. Ninety-seven per cent of NSW is in the most severe drought in living memory. The town of Murrurundi in the Upper Hunter has run out of water completely and is carting in water for that community," Ms McKay said.

"And what is the member for the Upper Hunter doing? What is he saying? Well, he's in the chamber and he's saying, 'I'm sitting in the chamber with a hard-on now.'

"Two days later during question time when we're discussing regional health, regional transport, we're discussing the budget of Fire and Rescue, what is Michael Johnsen doing?

"He's texting, 'I'm in QT [question time] right now and eff I'm horny and want you so bad. I want you and can't wait to eff you over and over again.'

"And then, when question time is finished, he takes himself into the nearest toilet, he masturbates, he films himself and he sends that message to a woman."

The woman at the centre of the allegations told the ABC she had exchanged hundreds of messages with Mr Johnsen after responding to his online advertisement for sex in August 2019.

The ABC matched the dates and times of the text messages with video of parliamentary sessions.

In one exchange on September 9, 2019, Mr Johnsen allegedly invited her to attend Parliament the next day.

"I have budget estimates scheduled between 9.30-12.30 tomorrow," he wrote. "My PH office could be fun."

He told her to wait for him in the Jubilee Room at Parliament, but she cancelled the rendezvous the next day.

The ABC said that on September 26, 2019, Mr Johnsen texted the woman for more than two hours while he was in Parliament for the passing of the NSW Reproductive Health Bill.

"I'm in QT and f*** I'm horny and want you so bad - need you, I want you and I can't wait to f*** you over and over again xxx," the report quoted him as texting.

The ABC said he had sent her a video at 3.53pm that day of a man appearing to masturbate himself in a toilet. The man is holding a tablet displaying an image of the woman in his hand.

Ms Berejiklian, when asked about the report on Sydney radio 2GB on Tuesday, said: "If that is correct, I am absolutely disgusted."

Mr Johnsen issued a statement on Wednesday last week saying he was "devastated" by the allegation that he raped the woman.

"I have voluntarily spoken with NSW Police and I have and will continue to fully cooperate with their inquiries," he said. "I am confident that any investigation will conclude that I am an innocent party."

The Nationals MP said in last week's statement that, "without admission", he was taking leave immediately "for a short duration".

An expulsion vote, used only four times in NSW Parliament's history, would require MPs to return from the start of a five-week break to debate the matter.

The last time the lower house expelled someone was in 1917.

The upper house expelled Country Party MP Alexander Armstrong in 1969 after a court found he had threatened to have a business associate killed.

A parliamentary briefing paper in 2003 said both houses had the power to expel members if their conduct prevented Parliament from exercising its functions with "mutual respect, trust and candour"; "caused to be suspect its honour and good faith of its deliberations"; or brought it into disrepute "and would lower its authority and dignity".