Asylum-seekers as young as nine have attempted suicide while in Australian immigration lock-ups, the peak medical body said as it slammed detention of youngsters as akin to "child abuse".

The Australian Medical Association said on Monday it was worried about the mental health of detainees, and that children were suffering from depression and self-harm.

"We are aware of a nine-year-old child who was recently admitted for trying to commit suicide," Peter Morris from the association's Northern Territory branch told an inquiry into the detention system, The Australian reported.

"The emergency department has also reported large numbers of adults with mental health problems manifesting in self-harm," in comments he confirmed to AFP.

Australia has long had a policy of mandatory detention for boatpeople seeking asylum and many are held in remote facilities, including on the Indian Ocean outpost of Christmas Island.

The government has softened its stance in recent years to allow more women and children into the community as their refugee claims are assessed but Morris recommended minors not be held in detention for more than three days.

"We agree that detention of asylum-seeker children and their families is a form of child abuse," he said.

"Mandatory detention is medically harmful, violates human rights, has no known beneficial effects and is a waste of money."

Some 845 minors, including those living in community accommodation, are among more than 4,700 boatpeople in Australian immigration detention.

Though they arrive in relatively low numbers by global standards, refugees are a thorny political issue in Australia, and a record influx last year of almost 7,000 boatpeople stretched facilities.