A letter was sent to Mr Morrison, as well as Labor's leader in the senate Penny Wong and Senator Sarah Hanson-Young on Friday, alleging rape by a senior minister before he entered politics.

The letter came with a detailed statement attached, prepared by the complainant for her lawyer, ABC's Four Corners has reported.

The complainant is no longer alive.

A spokesperson for Mr Morrison on Friday evening said any allegations should be referred to the Australian Federal Police.

"As per the AFP Commissioner's instruction, any complaints or allegations of this nature made to anybody - whether they're parliamentarians or journalists - should be referred to the AFP," the statement said.

The AFP on Saturday issued a statement saying it would liaise with the relevant state authorities.

"Further enquiries can be directed to the New South Wales Police Force," it said.

"The AFP will not be making further comment."

Senators Hanson-Young and Wong both released statements saying they had contacted the AFP about the letter.

Senator Hanson-Young said the information she had received regarded a "disturbing and a very serious allegation of a criminal nature against a senior member of the government".

Senator Wong said it was her understanding the complainant, who was 16 at the time of the alleged attack in Sydney, reported the assault to NSW Police and South Australia Police.

Four Corners says the woman reported the alleged rape to NSW police in February 2020, but took her own life in June after informing them she no longer wanted to proceed with the complaint.

NSW Police said in a statement on Friday night that a report of alleged historic sexual violence was received in February 2020 and detectives commenced an investigation under Strike Force Wyndarra.

"After strike force investigators were advised that the body of a 49-year-old woman was located at a home at Adelaide by South Australia Police (SAPOL) on Wednesday 24 June 2020, the investigation was suspended," the statement said.

The explosive revelations come a fortnight after former Liberal staffer Brittany Higgins' rape allegation engulfed parliamentary sittings, prompting Australia's major political parties to back a cultural overhaul.

The Morrison government has been under intense pressure over its response to the 2019 incident, in which Ms Higgins alleges she was sexually assaulted by a former colleague in Parliament House.

There are four inquiries under way including a multi-party investigation aimed at ensuring parliament is a safe working environment.

Labor's national executive on Friday adopted a code of conduct and three policies dealing with sexual harassment prevention and response, harassment and bullying, and complaints handling.

Ms Higgins is pushing for change after feeling she wasn't supported when she first made the allegation, leading to her withdrawing her police complaint out of fear for her job.

She reinstated the complaint on Wednesday and an investigation is under way.

Defence Minister Linda Reynolds was released from hospital on Friday after being admitted on advice of her cardiologist.

Senator Reynolds, who was Ms Higgins' boss at the time of the incident, was under extreme scrutiny about her handling of the complaint.

Australian Associated Press