Andrew Falloon, a first-term South Island MP, has resigned from parliament and may yet face criminal charges for his actions.

On Monday, Mr Falloon announced he would not re-contest his seat at September 19’s election when it emerged he sent an unsought explicit image to a 19-year-old university student.

On Tuesday morning, Mr Falloon took heed of a call from his leader Judith Collins to resign from parliament immediately.

“I am absolutely appalled by what I have been hearing this morning and finding out from members of the public,” she said, labelling him a disgrace.

News outlets Stuff and Newshub have alleged Mr Falloon, 37, has acted similarly to other young women, and Ms Collins said it appeared part of a “pattern of behaviour”.

“I’m sorry to say I believe we are going to have more women come forward,” she said.

“If I’ve already had two, to the office this morning, there will be more, and I’ve certainly had indications from people that they know of more.”

National was alerted to Mr Falloon’s behaviour by Jacinda Ardern’s office, after a complaint sent to the PM’s office was privately re-directed to the opposition.

Ms Collins summoned Mr Falloon for a face-to-face confession on Monday morning, but now believes the Rangitata MP was not telling the truth.

“I think it’s very obvious he lied to police and lied to a lot of people … and probably including himself,” she said.

Police had previously said Mr Falloon’s behaviour fell short of a criminal offence but Ms Collins said they were likely to revisit the matter.

Mr Falloon hasn’t spoken since news of his behaviour came to light, issuing a statement on Monday afternoon that a friend’s recent suicide had resurfaced personal traumas.

“I have made a number of mistakes and I apologise to those who have been affected,” he said.

Ms Collins said he had been escorted from parliament to the airport by an MP and picked up from airport by another MP, saying he was deeply mentally unwell.

“I was very deeply concerned for the welfare of the young woman involved, but I was also deeply concerned with the safety of Andrew Falloon. He is still a human being,” she said.

The scandal is another sorry chapter for the opposition less than two months before a national election.

Last week, Todd Muller shocked his partyroom by resigning the leadership, citing mental health, after just 53 days in the top job – the shortest spell for any elected party leader in NZ history.

Mr Falloon is one of 13 elected National MPs to not be facing the voters in September, including several star women – Nikki Kaye, Amy Adams and Paula Bennett – who are choosing to end their careers on their own terms.

-AAP