The fate of people housed on Manus Island that will not be resettled in Papua New Guinea or the United States is unclear, with neither the Australian nor PNG governments able to explain what will happen to them.

Key points: Many refugees "not willing" to stay in PNG, Peter O'Neill says

Many refugees "not willing" to stay in PNG, Peter O'Neill says Australia "working to solutions", Malcolm Turnbull says

Australia "working to solutions", Malcolm Turnbull says US Department of Homeland Security putting refugees under "extreme vetting"

Australia reached a deal with the United States last year to resettle 1,250 refugees from its offshore detention centres on Manus Island and Nauru.

There are more than 600 men on Manus Island, in PNG's north, and more than 900 on Nauru.

They are undergoing "extreme vetting" to establish whether they are eligible to be resettled in the US.

During a visit to PNG, Prime Minister Malcolm Turnbull and his counterpart Peter O'Neill were questioned about the fate of those who would not travel to the United States.

Mr O'Neill said some refugees had already been resettled in his country.

"But as you know, many of the refugees are not willing to resettle in PNG," he said.

"We cannot force people in a resettlement exercise when they are not able to accept our offer.

"But if a third country is willing to accept their resettlement, we're quite happy to participate in that."

What is the US-Australia agreement? Agreement would cover people on Manus Island and Nauru found to be genuine refugees.

Agreement would cover people on Manus Island and Nauru found to be genuine refugees. Depending on how many pass US's "extreme vetting" process, the ABC understands the offer would be made to the vast majority of people still in offshore detention centres, as well as those processed offshore but are currently in Australia due to medical reasons.

Depending on how many pass US's "extreme vetting" process, the ABC understands the offer would be made to the vast majority of people still in offshore detention centres, as well as those processed offshore but are currently in Australia due to medical reasons. The offer would not be made to those who have accepted resettlement elsewhere.

The offer would not be made to those who have accepted resettlement elsewhere. Federal Government has said it would prioritise families first.

Mr Turnbull was non-committal when asked who would take responsibility for those who were not offered resettlement in the United States and who refused to settle in PNG.

"We are working to solutions, durable solutions for the people who have been detained here, and indeed in Nauru, and we're working with third countries, most notably of course the United States to that regard," he said.

"But we'll take this process one step at a time."

Officials from the US Department of Homeland Security have been on Manus Island fingerprinting and photographing refugees, after interviewing around 300 people there earlier this year.

All refugees will have to meet "extreme vetting" requirements being implemented by the Trump administration in the US, even thought the specifics of those requirements are not known.