The Prime Minister could not say how many of the 1600 detainees on Manus Island and Nauru would be destined for the US, but predicted a "substantial" number would be eligible.  

He revealed that secret discussions on the deal, which was formally announced on Sunday, had been under way since January.

The "one-off" deal will only apply to asylum seekers currently on Nauru and Manus Island, and will also see a stepping up of Australia's on-water border control operations to dissuade people smugglers, who are expected to reopen the smuggling route once the asylum seekers are moved to a developed country.

Speaking to this former chief of staff, the conservative commentator Chris Kenny on Sunday night, Mr Turnbull told Sky he did not raise the matter with Mr Trump, who has pledged to ban Muslim immigration and curb Mexican migration, during their phone call on Wednesday.

"I deal with one administration at a time," said Mr Turnbull. "The United States government meets its commitments from one administration to another."

The head of a prominent US think tank has predicted a "firestorm" of opposition to the resettlement deal, calling it "the kind of thing the Trump administration will nix on day one".

"I don't expect any Republicans will defend it; I can't see a lot of Democrats defending it either. My sense is that when the word gets out on this, it'll be dead on arrival," Mark Krikorian, executive director of the Centre for Immigration Studies, told Fairfax Media.

He said discussions with the US government began with a personal discussion he had with President Barack Obama in January.

He said the agreement had to be read in the context of the "long history of cooperation on issues including national security" between Australia and the United States.

"The timing will be in the hands of the United States," he told Nine's Today program on Monday.

As it stands, there are 1600 detainees from the two centres who have been granted refugee status. The US quota will face health and security checks and come from within their existing annual intake.

"We have not set a number on it. The Americans will assess the refugees from a security and health point of view as referred to them," Mr Turnbull said.

Immigration Minister Peter Dutton told ABC that it was "hard to say" how many would be resettled in the US and that Australia was in "tentative conversation" with other countries about similar arrangements.

Mr Trump has threatened a trade war with China and an isolationist approach to foreign policy, which could leave Australia to do the heavy lifting in the Asia-Pacific region at a time when China is becoming increasingly assertive in the South China Sea.

But Mr Turnbull played down fears of a US-China trade war.

"In my job there's plenty to get worried about but I'm confident that the commercial relationships, economic relationships, will be managed in the national interest and it's clearly not in America's national interest to have some sort of economic cataclysm," he said.

Mr Turnbull repeated his suggestion that much of Mr Trump's election campaign rhetoric would not be met in government.

"I've been very careful not to make comments about Donald Trump or run a commentary on his policies because we'll see," he said.

"The one thing he knows ... and that Americans know – but I know Mr Trump knows this very well – (is) that we are a very good friend, a very strong ally and we are always very honest and frank with each other and he knows that."

And he said the president-elect had been impressed by Australia's naval expansion.

Mr Turnbull said as part of the asylum seeker deal with the United States, Australia's border patrols would be boosted. He said the government had sought "additional maritime assets" not long after he became prime minister in the leadership coup of September 2015.

"We needed to put in place all of the on-water measures ... to ensure that we were able to respond in the event that that people smugglers tried to use this as a marketing opportunity," he said.

"We'd rather overcompensate in terms of our response capacity than underdo it."

He pressed Opposition Leader Bill Shorten to back his new legislation that will ban for life any refugee who attempted to travel to Australia by boat from receiving a tourist or business visa.

Labor is opposing the move because it believes denying refugees lifetime access to Australia is a political tactic rather than a deterrent from the government.

Mr Turnbull said any future immigration minister would have a discretionary powers to waive the visa ban.

He also responded to the decision of the Sydney Mardi Gras to "uninvite" him from the official party next year because of his failure to implement same sex marriage.

"I've had so many invitations to go to their Mardi Gras parties ... we'll have no shortage," he said.

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