SYDNEY (BLOOMBERG) - Australian police are looking into an alleged rape that occurred decades ago and is said to have involved a minister now in Prime Minister Scott Morrison's government.

Federal police said in a statement on Saturday (Feb 27) that it received a complaint in relation to a historic sexual assault and will be liaising with the state authorities, without providing further details on the alleged assailant.

The assault took place in 1988, ABC's Four Corners news programme reported, citing an anonymous letter shared by a source close to the alleged victim.

Two senators said they received a copy of the complaint which involved a senior member of the federal government, adding that it was also sent to the Prime Minister.

Opposition Labor Party Senate leader Penny Wong said it was a rape that took place "many years earlier", while Greens Senator Sarah Hanson-Young called the allegation "disturbing" and of a "criminal nature".

The revelation comes less than two weeks after Mr Morrison ordered a probe into workplace culture at Parliament House, after a former government media adviser said she had been raped in the building by a fellow staffer in 2019.

Asked whether the minister involved should stand aside, Finance Minister Simon Birmingham said on Saturday that processes needed to be followed.

"Everybody is entitled to natural justice, and it's important to back the police to do their job," he told reporters in Adelaide. "We have to go back to the appropriate authorities, the police, to do everything they can to investigate and to their satisfaction, determine the appropriate course, forward, free of any sense of political interference or direction."

Ms Wong said on Saturday that her office had received the anonymous letter, which included what appeared to be a statement prepared by the complainant relating to the alleged rape. The woman who made the allegation died in June 2020, Ms Wong said.

Ms Wong said she had first become aware of the complainant's allegation when she ran into her in Adelaide in November 2019.

The complainant said that "she had been raped many years earlier by a person who is now a senior member of the federal government". The woman said she intended to report the matter to New South Wales Police, according to Ms Wong, who responded that she thought that was the right thing to do.

Ms Wong said she issued the statement "in the interests of transparency, and in the hope that appropriate action is taken to examine her allegation, the circumstances of her death and what can and should be done to help keep people safe and save lives in the future."