A Manus Island refugee is fighting for an injunction to keep the detention centre open, saying it is simply not safe for people to live outside.

Australia's detention facility in Papua New Guinea will permanently close this afternoon and the 600 men who have been refusing to leave have been told they must go.

Behrouz Boochani is seeking an injunction to keep the Manus Island detention centre open. ( Facebook: Behrouz Boochani )

Refugee Behrouz Boochani lodged an affidavit — which was witnessed by Australian Greens senator Nick McKim — in PNG's Supreme Court.

The PNG Government is urging the 600 men to move to accommodation provided at three sites in the main town of Lorengau.

But Mr Boochani said he and the other men feared for their safety if they had to leave.

"The police already, they beat some of the refugees and the local people. They attack the refugees and rob them. This place is not a safe place," he said.

In a final notice to the men inside the detention centre, posted overnight, PNG Immigration authorities said the facility would close at 5:00pm today.

The notice said the site would be returned to the PNG Defence Force and anyone choosing to remain would be liable for removal from an active military base.

The power and water will be cut off at 5:00pm, the food service will cease and all PNG immigration staff will depart.

The closure was announced after a PNG court ruled the detention facility was unconstitutional.

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Many refugees have already left the Manus Island detention centre, but about 600 remain. ( ABC News: Liam Fox )

This morning the ABC saw several busloads of Australian officials and workers heading to the island's airport with a police convoy.

A senior PNG immigration official confirmed all Australians working for the Australian Border Force and the contractors Broadspectrum and Wilson Security had left the detention centre.

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Mr Boochani tweeted that the notice was causing fear but said he and others were determined to stay citing concerns about their future.

Amnesty International Pacific researcher Kate Shuetze told the ABC the men were worried about how they would buy necessities such as food and medicine.

"Essentially there's no real plan here for them to be able to rebuild their lives, so that's really quite alarming," she said.

"We haven't heard anything from the Papua New Guinean Government as to whether these men would be allowed to work in the community and whether they're freely able to move around the country.

"In fact, we're hearing the opposite and all the indications around these new centres and the security around these new centres indicate that they're moving them from one prison to another with no logical rationale behind it."

Kon Karapanagiotidis, the founder and chief executive of the Asylum Seeker Resource Centre, said the closure would leave hundreds of refugees in "immediate serious danger".

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Immigration and Border Protection Minister Peter Dutton said the Coalition Government has had a clear and consistent policy since coming to office that anyone attempting to enter Australia illegally by boat would never settle here.

"The Illegal Martime Arrivals [IMA] who are refusing to leave the RPC have been aware since May this year that the PNG authorities would close the RPC today," Mr Dutton said.

Mr Dutton said detainees had been informed of safe and secure alternate accommodation where health and other services would be maintained.

Staff have already left the facility, which is due to permanently close at 5pm today. ( ABC News: Liam Fox )

Refugees will relocate to the East Lorengau Refugee Transit Centre of West Lorengau House and those found not to be refugees will relocate to Hillside Haus.

"The constant claims of IMAs and advocates about their situation in Manus are nothing more than subterfuge," Mr Dutton said.

"They have long claimed the Manus RPC was a 'hellhole' but the moment it was to be closed they demanded it be kept open.

"They claim to fear for their safety if they leave the RPC but held no such fears for a long period of time as around 200 of them each and every day travelled to and from Lorengau township, some staying in the town for extended periods of time."

Senator McKim, who has been visiting Manus Island, tweeted he had been granted permission to visit the centre on Tuesday afternoon and said the residents were "desperate people who want to be safe".

Mr Dutton slammed Senator McKim for claiming there was no alternative accommodation outside the RPC and said it was "false".

"Senator McKim's duplicity is breathtaking," he said.

"He sat through Senate Estimates hearings a week ago where officials from the Department of Immigration and Border Protection provided information in great detail about the facilities and services that would continue to be provided on Manus Island, but he chooses to ignore that factual information in favour of inaccurate and incorrect claims — it would seem — to incite trouble."