The Commonwealth Ombudsman is investigating concerns about sub-standard conditions and treatment at Australia's immigration detention centre on Nauru.

The investigation comes amid a growing number of complaints lodged by detainees and staff at the remote Pacific island centre.

Hania, a 32-year-old Christian Iranian, was in the Nauru detention centre for 10 months after she tried to catch a boat from Indonesia to Australia last year.

She told the ABC there was a lack of water and basic medicine in Nauru and said she had spoken to the Immigration Department, Salvation Army, Save The Children, International Health and Medical Services, and Wilson Security, which runs the centre.

"I mentioned a lot of things but none of them, they didn't care," she said.

Hania, who is several months pregnant, was in detention with her husband before being moved to Brisbane after a severe breakdown two months ago.

She said the final straw came when she witnessed parents at the centre beating their own children daily.

"In [one] tent there are different families with kids," Hania said.

"One of them, they just wrap their four-year-old girl with rope and beat her every day and she's screaming and screaming.

"The only thing they do is give valium to people who are suffering from depression and just keep them asleep."

A Salvation Army spokesman said the majority of Hania's claims arose at a time after the organisation finished its contract on Nauru and has denied the remainder of her complaints.

The Commonwealth Ombudsman is investigating Hania’s case but has referred the more serious allegations to the Nauruan government as it is not within its jurisdiction.

Detainee says guards propositioned her

Another Iranian woman, 27-year-old Ghazaleh, claims she was propositioned by guards during her five months on Nauru.

"Because we were females and we had no safety and security and no rights," Ghazaleh said.

"We came here to seek asylum and unfortunately this is the way we have been treated."

Local police were called to investigate allegations of sexual assault by Nauruan guards.

"They did some investigation about that, but they don't let people know," Hania said.

The sexual-assault allegations have been referred to Nauruan authorities.

Detainees and employees reporting poor conditions

Amnesty International spokeswoman Kate Schuetze said her colleagues were compiling similar reports from a range of sources and both detainees and employees at the centres had come forward.

"We've actually seen more whistleblowers willing to come forward and talk about what is actually happening in these centres," she said.

"Until they open things up and start to address some of those allegations in a manner which we can see is independent and fair, that shadow is going to remain."

An Iranian man named Saeed was detained on Nauru for months before being moved to Darwin for medical treatment after he suffered a stroke.

He said he was placed in solitary confinement because he complained too much.

"With just underwear I went inside the cell and on the floor of the cell there was a lot of blood," he said.

"The lights went all off because there was a blackout. I was really scared because it just went dark.

"I just know that I passed out and when I opened my eyes I was in hospital. My arm and leg are paralysed on the left side."

Representatives from Wilson Security and its contractor, Transfield Services, plus spokespeople from International Health and Medical Services and Save the Children all directed the ABC to Immigration Minister Scott Morrison's office for a response.

Mr Morrison declined to comment on the allegations and the Nauruan government is yet to respond to the claims.