Police on Manus Island say some of the staff at the island's Australian-run immigration detention centre are causing tension in the community by failing to respect Papua New Guinean law.

They said foreign staff working at the centre had been flown out of PNG before they could be questioned by police over a number of incidents, including the death of asylum-seeker Reza Barati and a possible sexual assault.

"It is an ongoing concern for me," Manus Provincial Police Commander Alex N'Drasal said.

"I am always frustrated when these things happen."

The most recent incident to anger local authorities was a serious car crash, in which two expatriate staff were injured.

Police said the two men were allowed to leave the island — Papua New Guinea's most remote province — for medical treatment.

Commander N'Drasal said they were meant to return for questioning and to face possible charges for drink-driving.

An incident in mid-July involving a local woman caused local police to threaten to arrest the centre managers if three men allegedly involved in the incident were not flown back to PNG.

"The incident is serious in nature," Commander N'Drasal said.

Manus Provincial Police commander Alex N'Drasal says he is frustrated with the situation. ( ABC )

"I believe it is similar to the Reza Barati case," he said, referring to police efforts to interview two expatriate staff allegedly involved in the death of the Iranian asylum-seeker at the centre last year.

A police investigator told a court hearing on Manus Island on September 25 that he had been unable to interview or charge two men, one Australian and one New Zealander, who were allegedly part of a group of men who attacked Reza Barati.

They had also been unable to interview the three men accused of involvement in the incident with the local woman because they flew out of the country shortly afterwards.

The Australian Department of Immigration and Border Protection said they were later stood down for failing to meet behavioural standards.

"He's not supposed to fly out because the investigation is on," the woman involved told the ABC.

"I want answers."

Police push to change detention centre operator's practices

The woman, a former employee at the centre, said she was found naked and passed out in a bathroom at the Wilson Security staff quarters.

"My concern is the way I was been found," she said.

"I'm not found in a good shape."

A former female employee at the centre said she was found naked and passed out in a bathroom at the Wilson Security staff quarters. ( ABC )

The woman had been socialising with Australian colleagues from the centre.

She said she believed she may have been sexually assaulted after one of the men gave her two pills.

The woman said she was not given a physical medical examination after the incident.

She was later suspended for breaching company rules that night, then resigned.

"It's been depressing," she said.

"It still is. I'm fighting it. Trying to be strong for it. But really, it's eating me."

Police want Australian company Transfield, which runs the centre, to change the practice of removing staff before they can be questioned.

The Australian Department of Immigration and Border Protection did not respond to the ABC's questions about these issues.