Docs don't get veto on detention returns

The immigration department's chief medical officer has admitted detention is bad for the health and welfare of children.

"The scientific evidence is that detention affects the mental state of children - it's deleterious - for that reason, wherever possible children should not be in detention," Dr John Brayley told a Senate estimates hearing on Monday.

Doctors do not get to decide whether asylum seekers receiving medical attention in Australia are sent back to detention centres on Nauru or Manus Island, the hearing was told.

The Department of Immigration Secretary Michael Pezzullo insisted doctors provide advice that was acted on.

"We all go to hospital, we're seen by three or four different doctors, they are a bit like lawyers from time to time, they've got five or six different opinions," he said.

The department had access to medical experts to assess whether "on balance" the appropriate care could be provided on Nauru.

A $26 million upgrade of the Nauru hospital, a gift from Australia to the Pacific Island, will have pediatric, cancer, emergency and obstetric facilities, the hearing was told.

Meanwhile, Border Force Commissioner Roman Quaedvlieg told the hearing he was concerned post traumatic stress disorder may manifest in some staff involved in maritime operations rescuing asylum seekers more than three years ago.

He said the staff were generally a resilient bunch, however, Dr Brayley would turn his clinical attention to the matter to look at preventative measures.