Police on Manus Island have confirmed an asylum seeker has died overnight.

A 32-year-old Sri Lankan Tamil man was found near the kitchen of the Lorengau Hospital after reports he was mentally unwell.

Friends of the man said it appeared he took his own life and Australian authorities have confirmed the death.

"The department is aware of the death at Lorengau Hospital," a spokesman for the Department of Immigration and Border Protection said.

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The man was staying in a so-called "transit centre" near the main town on Manus Island.

Friends of the man said he had been distressed and anxious for some time and his body was found at 4:00am near a kitchen in the complex.

Sri Lankan refugee Shamindan Kanapadhi was the man's friend and said he had not been given adequate care.

"Three days ago he cut his neck and they take him to the hospital and he hasn't been given any proper treatment," he said.

The man was charged with sexually assaulting a local woman in January, but denied any wrongdoing.

Refugees said there were several other men at the centre with serious mental health problems who were not getting any care.

Sister Jane Keogh is an Australian Brigidine nun who is on Manus Island. She said she spent her Sunday trying to get treatment for another Sri Lankan refugee who was having a psychotic episode but the situation was dire.

"I think it's high level. If the people at the hospital are saying there are three cases of psychosis at the moment, well psychosis, you don't know what they're going to do next," she said.

"If people can run naked through the town and no-one's allowed to apprehend them or do anything with them, probably the police could put them in the lock-up which would only add to their trauma, any of those three could die, imminently."

'Tragedy imminently foreseeable'

Greens Senator Nick McKim said indefinite detention was designed to cause mental anguish.

"When you design a system of indefinite detention, a system that has created and designed deliberately to cause mental harm, mental anguish and trauma, this kind of tragedy is imminently foreseeable," he said.

However, the Australian Government deferred responsibility to the PNG authorities with Foreign Minister Julie Bishop saying she had little information.

"I am aware of reports that a person has died in a PNG hospital. There will obviously be an investigation by PNG authorities but I suggest that the PNG authorities speak on this matter. It occurred in PNG. I have no other information," she said.

The latest death is the second apparent suicide in the transit centre in the last two months.

Iranian asylum-seeker Hamed Shamshiripour was found dead nearby in August.

Six detainees from Manus Island have died since 2013, when Australia began its policy of not resettling boat arrivals processed offshore.

This latest death comes as Australian and PNG authorities move ahead with plans to close the Manus Island detention centre by October 31.

The refugees inside have been told to move to alternative accommodation, mainly the transit centre, so the detention centre can be shut down.

On September 26, 25 men from Manus Island were the first offshore detainees to be flown to the United States for resettlement there, under a deal struck between Australian Prime Minister Malcolm Turnbull and US President Barack Obama.

Reverend John Daniel Jegasothy — who leads the Uniting Church's Tamil congregation in Sydney's west — said the uncertainty for those left behind was cruel.

He said the Federal Government had a duty of care and after such a long time they deserved to come back to Australia.

Dr Jegasothy said with the centre closing by the end of the month, people were feeling desperate.