Australia has said it remains committed to resettling 12,000 Syrian refugees, but warned painstaking security checks could take more than a year.

The government said in September that the refugees would be resettled as quickly as possible but Liberal MP Cory Bernardi said the cabinet should rethink that commitment in light of the risk that terrorists could pose as refugees.

Cabinet ministers including treasurer Scott Morrison and counter-terrorism minister Michael Keenan stood by the government's decision.

Peter Shergold, co-ordinator general for refugee resettlement in New South Wales, said the resettlement process could take from 12 to 18 months because of the careful screening.

The Syrian refugee intake is on top of Australia's usual annual intake of 13,750 refugees from around the world.