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

The Australian Medical Association (AMA) said it was worried about the of detainees, and that children were suffering from depression and self-harm. Some had also gone on hunger strike.

"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 has also reported large numbers of adults with manifesting in self-harm," he said 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 families not be held in detention at all.

"Our view is that unnecessary detention is the equivalent of child abuse and that's been a view held by in the field for many years," he told AFP.

"The big issue is that children and their families should not be in detention. It's unnecessary. These people do not pose a real security or . And a long detention is harmful and a waste of money."

Morris said the average detention time was close to a year and studies around the world, including in Australia, had shown rates of depression among asylum-seeker children in detention were as high as 30 percent.

In May, Darwin doctors reported that asylum-seeker children were attempting self-harm and even suicide.

"There's definitely been cases of attempted suicide and even cases of some young children taking up hunger strikes," AMA Northern Territory president Paul Bauert said at the time.

The Royal Darwin Hospital confirmed to the inquiry Monday that in the 12 months to the end of the July, there were 33 children up to the age of 16 discharged from the hospital, among them some cases of self-harm.

Refugee advocates say there have been five suicides in immigration detention nationally, all adults, since September 2010, but report many "near-miss" cases among despairing inmates.

The government has already announced a probe after more than 1,100 cases of threatened or actual self-harm were reported in a year.

The AMA has previously called for quick action to stop deaths and injuries in immigration centres which this year have seen detainees stitch their lips together, go on hunger strikes and stage violent confrontations.

"The AMA believes that the system of mandatory detention of asylum-seekers is inherently harmful to the physical and mental health of detainees," national president Steve Hambleton said last month.

"The harm is especially acute in the case of children."

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.