Australia is creating widespread depression among asylum seekers by systematically locking them up, the United Nations has said.

Illegal immigrants are treated worse than criminals because they are not told how long they will be held, said a UN delegation.

Woomera camp is in the remote outback

The UN officials have spent two weeks inspecting Australia's five detention camps, including the notorious Woomera centre, scene of riots, break-outs, attempted suicides and mass hunger strikes.

All illegal immigrants including young children are detained while their asylum claims are processed - and that can take up to five years.

"The detainees live day in, day out, with an agonising uncertainty about the duration of their detention," said Louis Joinet, chairman of the UN Working Group on Arbitrary Detention.

He said the situation at Woomera camp, in the South Australia desert was "dramatic" and the camps - which are surrounded by high fences topped with barbed wire - were by no means "luxury prisons".

'Serious concerns'

Australia has already announced that Woomera is to be scaled down and another camp closed once new, more modern centres are built.

This time in detention is something that doesn't happen to common criminals

Louis Joinet, UN

And on Thursday, Immigration Minister Philip Ruddock again defended Australia's asylum policy, saying "no substantive issues" were raised during his talks with the UN visitors.

He said the detainees tried to exploit such visits as opportunities to "impress their claims upon individuals whereby they then seek to self-harm and exhibit what some people call 'collective depression'".

Bu Mr Joinet said he had serious concerns about the asylum seekers "particularly young children, unaccompanied minors, persons with disabilities, pregnant women and of course the elderly.

"This time in detention is something that doesn't happen to common criminals when they're put in prison because their time is limited by law," Mr Joinet said.

"The process is very slow and also there's a lack of adequate information given to detainees on the status of their visa applications, with the result that it appears they are almost living in limbo."