Malcolm Turnbull has delivered his strongest comments yet in the wake of the Manus Island court ruling, saying detainees will not be resettled in Australia and warning against being "misty-eyed" about the policy.

Key points: Prime Minister says Government needed to be "clear and determined in our national purpose"

Prime Minister says Government needed to be "clear and determined in our national purpose" Peter Dutton says Australia "had discussions with Nauru"

Peter Dutton says Australia "had discussions with Nauru" Labor says Coalition should negotiate with PNG about changing laws

The Prime Minister made the comments amid ongoing speculation about the future of about 850 detainees at Manus Island detention centre, which the Papua New Guinea Supreme Court ruled as illegal earlier this week.

PNG's Prime Minister Peter O'Neill intends to close the centre and Mr Turnbull has emphatically ruled out any of the men coming to Australia.

"They will not come to Australia — that is absolutely clear and the PNG Government knows that," he said.

"I look forward to discussions with the PNG Government, but there will be no transfer of those individuals to Australia."

Mr Turnbull also emphasised the record of the former Labor government, citing "50,000 unauthorised arrivals" and "thousands of deaths at sea".

"We cannot be misty-eyed about this," he said.

"We have to be very clear and determined in our national purpose... We must have secure borders and we do and we will, and they will remain so, as long as I am the Prime Minister of this country."

Immigration Minister Peter Dutton said the Prime Minister had been "rock solid" on this position, though the option of transferring Manus Island detainees to upgraded facilities on Christmas Island has been left open.

Mr Dutton has refused to be drawn on the option of using Christmas Island as an alternative place of detention but did not rule it out today.

"I just don't think we need to be talking about Christmas Island or Nauru or anywhere else," he told radio station 2GB.

Nauru centre has room for Manus Island detainees

Sorry, this video has expired Turnbull warns against being 'misty-eyed' on offshore detention

He made the comment in the context of continuing negotiations with Papua New Guinea's Government, including the option of an "open-centre-style arrangement" on PNG.

The Immigration Minister late last year said that preparations were underway to accommodate more asylum seekers at Christmas Island, in case the Government lost a High Court case being fought in Australia.

The Government won that case, though "prep work" at the centre was carried out.

Today Mr Dutton also confirmed there was capacity for the remaining Manus Island detainees to be transferred to Nauru.

"We've had discussions with Nauru," he said.

"There's obviously capacity across the network, including on Nauru."

PNG law change, money could keep centre open: Marles

Labor's immigration spokesman Richard Marles wants the Australian Government to try to convince the PNG Government to keep the centre open.

He has suggested negotiating with Mr O'Neill about changing the country's laws to make detention legal or offering more money.

"All of those options need to be talked through with the PNG Government," he said.

PNG officials are preparing to travel to Australia early next week for fresh negotiations about the future of the detainees and the country's High Commissioner to Australia, Charles Lepani, said the centre would not close immediately.

Manus Island MP Ronnie Knight told Radio National he expected Australia to keep funding projects it agreed to as part of the detention centre deal.

"Fulfilling their part of the agreement to continue to finish our roads and do what they promised," he said.

He warned of consequences if Australia withdraws from those projects.

"If they do that then maybe next time down the track when they ask for help again it might be the other way around. We won't assist them," he said.