Showdown looming on Manus Island

A showdown is looming on Manus Island, with Papua New Guinean authorities warning barricaded refugees to get out within two days or be moved by force.

Almost 600 men have been holed up inside the mothballed detention facility, more than a week after it was shut down.

Despite running out of food, medication and drinking water they believe it's safer to remain in the compound than risk being attacked by locals at new facilities near the main township of Lorengau.

PNG authorities posted a warning notice on Thursday.

"You are... instructed to vacate this compound immediately," the memo says.

"If necessary, force may be used to relocate those who refuse to move voluntarily for your own sake."

Demolition of fences will take place on Thursday.

Iranian refugee Behrouz Boochani said the use of force was unacceptable.

"We are not doing anything wrong, we are only resisting peacefully," he told AAP.

"We are asking again for freedom in a safe third country."

Greens senator Nick McKim is en route to Manus Island on Thursday to witness the eviction.

Labor's immigration spokesman Shayne Neumann defended his decision not to visit Manus Island and suggested the senator's attendance may be unhelpful.

He thinks the refugees should just move to the alternative accommodation.

"The best advice I have ... is that my presence, or even Nick McKim's or even the minister, will not actually act to de-escalate the tension," Mr Neumann told ABC Radio.

"I'm not about to engage in political tourism in relation to this issue."

Senator McKim said the treatment of the men was Australia's most egregious violation of human rights in his lifetime.

"I know from talking to the guys in the camp that they are very appreciative of my visits to Manus Island and I'm here to support them in the choices they have made," he told AAP.

The UN's refugee agency says substantial parts of the alternative accommodation are not yet ready.

Mr Dutton insists those claims are wrong.

"The only difference in the new centre is that where we serve three meals a day at the (detention centre), we're asking people to prepare their own meals with food supplied and some think that that's not good enough for them," he told 2GB.