US refugee vetting awaits Trump approval

The United States has not started vetting refugees it has agreed to take from Manus Island and Nauru under a deal struck with Australia.

The head of Australia's immigration department has told a Senate hearing American officials have begun preliminary screenings, but no refugees have cleared vetting requirements to go to the US.

Mike Pezzullo said the US government was still examining its vetting thresholds, with a review due to be returned to the White House "imminently" before the Trump administration gives the go ahead.

He expects vetting to begin "in the foreseeable future".

"Our colleagues in the Homeland Security department are poised and ready but they still need to await that authorisation (from the White House) to commence the vetting process," Mr Pezzullo told an estimates hearing at Parliament House.

"I'd be confident that there'd be movement within the next few several months."

Senator Michaelia Cash, representing the government, was asked whether there was a direct trade-off underpinning the US refugee deal after Peter Dutton stoked confusion on the issue last week.

"I would say on behalf of the minister that the arrangement is not a people swap deal," she said.

It also emerged the government was investigating mental illness among border force staff caused by intercepting asylum seeker boats.

Border Force Commissioner Roman Quadvlieg said he was "exceptionally concerned" about post-traumatic stress disorder among staff by "pulling dead bodies out of the water" and dealing with trauma on the front line.

"PTSD can lay dormant for significant periods of time and I suspect will have a long-lasting impact on our staff," he told the hearing.

The department says it knows of about 1200 deaths at sea from boats coming to Australia.

Earlier, Mr Pezzullo told the hearing he doesn't apply too much emotion to his work.

Mr Pezzullo was pressed about whether he was shocked by a damning audit into Manus Island and Nauru immigration contracts.

The Australian National Audit Office late last year released a report that highlighted sloppy record keeping and poor tendering within the immigration department over service provider contracts.

Mr Pezzullo conceded his department had been "fairly admonished" for the state of its records.

"I go about my work without putting too much emotion into it," he told senators.

"We go about our jobs in a clinical and unemotional fashion."