Shocking accounts of sexual assault and squalid living conditions at the Australian-funded detention centre on Nauru have been revealed in submissions to a Senate inquiry.

The inquiry was launched following the release of the independent Moss Report, which detailed sexual and physical assaults on asylum seekers.

The Senate committee's first public hearing is being held in Canberra today.

One submission from a doctor who recently visited the Pacific nation details an alleged rape against a woman going to the toilet at night.

"When interviewing the [patient] referred to me, she confided to me that she had been raped," Professor David Isaacs wrote.

"She told me that since the rape, one guard had offered her extra shower time in return for sexual favours.

"And on another occasion a different guard offered marijuana in return for sexual favours."

The Sydney-based Immigration Advice and Rights Centre (IARC) recounted the story of a female detainee who said her son had been sexually assaulted three times.

"In 2014 [the boy] began to self harm and was speaking about attempting suicide. It later became evident to [his mother that the boy] had been sexually assaulted," the submission reads.

The IARC submission also claimed Nauruan and Australian officials had had relationships with detainees.

Former Nauru magistrate, Australian Peter Law, said it appeared the country's police force had failed to properly investigate serious sexual and violent incidents against refugees and asylum seekers.

"The failure ... to bring charges suggests political interference and highlights an unwillingness to bring to public attention, the circumstances of refugees in Nauru generally," Mr Law's submission states.

"Such action may reflect adversely on Nauru as a place to process and settle asylum seekers."

Mr Law was deported from Nauru in 2014 after granting an injunction against the deportation of two people from the island.

Mouldy conditions cause fungal infections: submission

The submissions also shed light on the living conditions in the detention facility, with some describing mouldy tents full of cockroaches and rodents.

"At night, condensation causes the mould to drip onto the faces of people as they sleep on stretchers. This is causing fungal eye and skin infections," Asylum Seeker Resource Centre's submission reads.

"The tents are full of mice and cockroaches. Rats loiter outside the tents."

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Contractors Transfield Services, Wilson Security and the Immigration Department will appear at today's inquiry, along with charity Save the Children.

The department's submission explains the process that deals with complaints, while conceding the reporting of allegations needs improvement.

"All allegations of inappropriate behaviour at the Regional Processing Centre are taken seriously and are appropriately investigated," its submission reads.

"Allegations of criminal behaviour are referred to the Nauru Police Force who is responsible for investigating contraventions of Nauruan law.

"The Government of Nauru and the Department are committed to improving the mechanisms in place to capture all allegations, with a view to encouraging reporting and enhancing the effectiveness of current reporting systems to ensure information is readily accessible and accurate."

The Senate committee is due to hand down findings by the middle of June.