Evidence presented before a Senate committee at Parliament House on Tuesday included claims of guards trading cigarettes for sexual favours, and a woman being raped by a cleaner late at night on her way to the bathroom. Representatives from security company Transfield Services avoided questions about the serious allegations.

Instead, Transfield said it was  working on improving its "harassment and professional boundaries" policies. 

"Despite our commitment and our best efforts, some allegations of misconduct have arisen," said Kate Munnings, Transfield's chief executive of operations.

Brett McDonald, the security contract manager for Wilson Security, which is contracted by Transfield, said he was aware of at least one incident in which a "transferee had been mishandled", and "there have been some cases where staff have been moved on or terminated". 

The inquiry, which comprises two Labor senators, one Liberal senator and a Greens senator, heard that asylum seekers on Nauru were being held in mouldy tents in temperatures above 30 degrees, and local Wilson guards were not screened for working with children.

It also heard that neither the Immigration Department nor the Immigration Minister had apologised to Save the Children after accusing 10 staff of coaching asylum seekers to self-harm.

Tuesday's evidence differed from  an independent government report written by former integrity commissioner Philip Moss that found compelling evidence that at least three women had been raped inside the detention centre and said that sexual assault was likely to be under-reported due to a climate of fear and detainees worrying about their future refugee status.

Immigration Minister Peter Dutton was dismissive of the Senate inquiry, accusing the Greens and Labor of running a "political stunt" and "grandstanding" during Tuesday's hearing. He said the government would not tolerate sexual abuse where it had any influence.

David Isaacs, a doctor who worked briefly on the island, wrote in his submission to the inquiry that a woman had told him she had been raped by a cleaner when she went to the toilet at night.

"She told me that since the rape, one guard had offered her extra shower time in return for sexual favours (each person was restricted to two minutes a day because of water restrictions), and on another occasion a different guard offered marijuana in return for sexual favours," he wrote.

Transfield executive general manager Derek Osborne said he was "made aware" of the allegations of sexual abuse and the limited access to showers but could not say when.

The company could also not tell the committee what the gender breakdown was of its 275 expat guards and 277 local guards, how often there were power blackouts on the island, when it was t first told of the allegations of rapes or sexual assault, or how often its "whistleblower hotline" was used.

Questions on these topics were taken on notice.

When asked whether male guards were present when women were showering, Mr Osborne said: "No".

Wilson Security later confirmed male guards patrol the shower areas, but do not enter.

Greens immigration spokeswoman Sarah Hanson-Young said: "A seedy and toxic environment has been unveiled and it's clear the government has been trying hard to cover it up."

Fairfax Media understands Transfield Services was told about the hearing on Thursday night.

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