Prime Minister Scott Morrison says allegations against NSW Labor leader Luke Foley are "shocking and disturbing".

ABC journalist Ashleigh Raper has revealed details of a November 2016 incident in which the state opposition leader allegedly put his hand down her underpants.

"The alleged behaviour of Mr Foley is very, very shocking and concerning," Mr Morrison told reporters in Mackay on Thursday.

"They are matters for him and his colleagues in the Labor party to address, whether it's Bill Shorten or others.

"They are matters for them to reflect on. I'm not here to act as judge and jury on these sorts of things."

Earlier, federal Labor leader Bill Shorten described it as a "serious matter" but declined to comment further after the news broke while he was giving a press conference.

"I will go away and get acquainted on the facts," he told reporters in Perth.