A child asylum seeker who was allegedly raped on multiple occasions as a 10-year-old while detained on Nauru is suing the Federal Government over accusations it failed in its duty of care.

Lawyers for the Iranian boy claim he was raped three times by an older detainee at Nauru's immigration detention centre in September and October 2014, a year after he was transferred from Christmas Island.

According to a writ filed in the Victorian Supreme Court, the boy now exhibits suicidal tendencies and suffers from post-traumatic stress disorder, major depression and anxiety and requires ongoing medical treatment.

It alleges the Commonwealth and the detention centre's operators, Broadspectrum and Wilson, had a responsibility to provide a safe environment for the boy and should have known he would be at risk of being sexually assaulted by other detainees.

The writ claims there were inadequate protocols in place to ensure detainees were not sexually assaulted and that staff were adequately trained to deal with assaults.

Lawyer Dimi Ioannou from Maurice Blackburn, which is representing the boy pro bono, said she was concerned the authorities did not act immediately when the first alleged abuse was reported.

"The mother initially reported the assaults as soon as it happened, however … it wasn't until the third incident, when she again went back to the authorities and raised what happened to her little boy [that they acted]," she said.

"The authorities did not act fast enough."

The boy and his mother were flown from Nauru to Australia in October 2014 after the third alleged assault, according to the writ.

Ms Ioannou said the boy is traumatised and has nightmares about what occurred.

"He doesn't want to separate from his mother and he does live in fear," she said.

"He was only 10 years old when this incident happened."

Boy's court action to provide test case

Ms Ioannou said the boy's case is one of a number involving the alleged sexual assault of asylum seekers on Nauru that are currently being investigated by Maurice Blackburn.

"This case … is testing important legal questions regarding the duty of care owed by the Commonwealth and other defendants such as Broadspectrum and Wilson," she said.

"People in detention, particularly children, are very vulnerable and you have to ensure a safe environment.

"In our view that did not occur in this case."

The claim is seeking damages, interest and costs from the Federal Government, Broadspectrum and Wilson.

The Home Affairs Department and Broadspectrum have not responded to requests for comment.

In a statement, Wilson said it had not yet received the claim but would not provide any further comment on a matter before the court.