A Federal Opposition frontbencher has broken ranks and called for an end to "ongoing mandatory indefinite" offshore detention of asylum seekers.

Labor restarted offshore detention and established regional resettlement while in government, and both remain the party's official policy.

"I really think that the ongoing mandatory indefinite detention of people on Manus Island and Nauru has to stop," Senator Lisa Singh told Q&A.

"I think that the children need to be taken out of Nauru and our detention centres.

"There is no processing going on. It is indefinite detention and that is not humane.

"These are people that have ... fled persecution, they are refugees, they've been deemed refugees, and yet they've been left languishing in Manus Island and Nauru for years and years on end.

"I think we do need to have a new conversation about refugee policy in this country. I think it will be a dark mark on our history."

Senator Singh, Labor's shadow parliamentary secretary for the environment, climate change and water, is an unaligned member of the party's left faction.

Earlier this year she was relegated to fourth place on the party's Tasmanian Senate ticket for the next election, a position that is considered unwinnable.

Wyatt defends Government's approach, says children are being processed

The Government has been defending its record on children in detention over recent days, after it was revealed medical staff from Melbourne's Royal Children's Hospital refused to discharge some young asylum seekers back into detention.

It said fewer than 200 minors were being detained — down from a peak of almost 2,000 under the former Labor government.

"The process that Peter Dutton has in place means that people are being processed," Assistant Health Minister Ken Wyatt said.

"The processes that he's putting into place are moving towards the transferees having freedom on Nauru.

"We will continue to take a hardline [approach].

"There is a need to have in place strong measures that we will adhere to."