Australian police are investigating a claim that a female asylum seeker in detention on Christmas Island has been sexually assaulted by another asylum seeker.

The Christmas Island Shire President Gordon Thomson says that the woman was assaulted in one of the five family compounds on the island.

The matter was reported late last week after the woman came forward to make a complaint.

"There is an allegation that a woman was raped in the aqua compound which is one of the five family compounds on Christmas Island," he said, adding that aqua and lilac compounds are notoriously in bad condition.

Mr Thomson says it is not clear if any charges have been laid as everyone is "very tight lipped about information to do with anything happening at the immigration detention centre on Christmas Island".

"But I understand the allegation of rape was reported to Serco on Saturday and police have interviewed the person who made the allegation of rape," he said.

Staffing issues

Mr Thomson says issues with staffing levels is the key reason why these incidents are happening.

"There are issues about staffing levels, there are large number of people in the compound," he said.

"There are concerns that a lot of single women in the compound have expressed concerns to their department of immigration case managers about the imminent arrival of large number of young adult males.

"They are concerned for their safety."

There has been a rising concern with overcrowding, with more than 2,200 asylum seekers now being held on the Indian Ocean territory.

And some cases of poor sanitary conditions are adding to the frustrations of people living through another hot and humid wet season.

A spokesman for Australia's Immigration Minister Scott Morrison says there are no plans to transfer any more single adult males into the same compound.

"The detention services provider is required under contract to provide appropriate staffing resources consistent with the detainee caseload at any given time," he said.

"There is absolutely no plan to move single adult males into family centres on Christmas Island."

But Christmas Island locals say tension is rising over plans to move some single men into these family areas under a family reunion program.

There are currently 11 staff members at night on the compound, according to Mr Thomson, who says it is "inadequate".

Accurate numbers of asylum seekers in each compound are not available but Mr Thomson estimates it to be "hundreds of people in the aqua and lilac detention centres".

"We have a situation where if anybody is off sick, they are not replaced. And the number of 11 on the night shift for example is reduced by the number of people who might be off work for any number of reasons," he said.

"The issue is that if you have... inadequate staffing levels in our opinion, there is less supervision.

"The connection between staffing levels and concerns about safety must be made."

"If people have a concern, and those concerns have been expressed by many young single women in the family compounds, they have expressed their concerns, their fears for their safety, the question is have those fears expressed been properly dealt with?

In our opinion, it does not enhance the security of those young women who have... expressed their concern," Mr Thomson said.