The last four children living in Australia’s asylum seeker processing centre on Nauru have been flown to the US for resettlement.

The children left the island country with their families on Wednesday afternoon.

Immigration Minister David Coleman said the milestone comes after there were 2000 children living in detention when the coalition formed government in 2013.

“We got them all out,” he said on Thursday.

“This is something the Government has been working on for some time, quietly and in a way that would not impact our border protection policies.”

The departure of the children and their families brings the number of refugees to have been resettled in the US under a deal with Australia to 493.

Another 265 refugees have been assessed but rejected by the US under its extreme vetting policy.

At the moment, 394 asylum seekers remain on Nauru and 580 on Papua New Guinea’s Manus Island.

Some refugee advocates are worried the US deal won’t allow resettlement for the hundreds of asylum seekers still on Nauru and that the Government is “dragging its feet” on medical transfers for those who are sick.

“Almost six years of detention on Nauru has created a mental health crisis on the island, and the Government still has no secure future for them,” Refugee Action Coalition spokesman Ian Rintoul said.

But Home Affairs Minister Peter Dutton said Australians had been “conned” into believing medical care on Nauru and Manus Island was not being provided to those who need it.

His comments come after changes pushed by Labor and crossbenchers passed parliament without the government’s support earlier this month, making medical transfers for asylum seekers easier.

“We’re being conned,” Mr Dutton told Sydney radio station 2GB on Thursday.

“The true story of Manus and Nauru is going to come out at some point.”

Mr Dutton said he was focused on ensuring the changes did not ramp up the people-smuggling trade.

“This is a very dangerous period in our border protection policy,” he said.

The Government plans to send sick people from Manus Island and Nauru to Christmas Island, but Labor is concerned about whether they will receive adequate care.

-AAP