The chief rights advocate for the United Nations has expressed alarm at a new push by Australian immigration authorities to immediately reject a number of Sri Lankan asylum seekers.

UN High Commissioner for Human Rights Navi Pillay is in Bali for a democracy summit, also attended by Prime Minister Julia Gillard.

Ms Pillay said she had heard numerous concerns that asylum seekers could languish indefinitely on Nauru and Manus Island under Labor’s revived Pacific Solution and was especially worried over the plight of children.

‘‘I am highly concerned that detention in regional offshore processing centres such as in Nauru could result in indefinite detention and other human rights violations,’’ she said.

‘‘All people, including migrants, have the right to the highest attainable standard of physical and mental health, and this form of detention has been shown at times to violate this right.

‘‘It could well end up as indefinite detention, and people in indefinite detention suffer significant mental health issues - and Australia should be well aware of this.’’

The number of people arriving in recent months has already far exceeded the planned capacity for the two centres in the Pacific.

In a bid to toughen the deterrent, Labor plans to remove the Australian mainland from the migration zone.

The Immigration Department has sent home dozens of Sri Lankans - from Christmas and Cocos islands - deemed not to have a refugee claim.

But Ms Pillay said Sri Lanka was still volatile, despite the end of the civil war in 2009.

‘‘Now that was a conflict area, matters have not stabilised as yet.

‘‘All the reports reaching me are that people are concerned over controls being imposed over them,’’ she said.

‘‘So I can understand if they’d be leaving out of fear or for their personal security, and it really cries out for all the refugee protections, asylum seeker protections to be made particularly applicable to them.’’

Ms Pillay visited Australia last year, meeting with Ms Gillard, and visiting detention centres in the country.

‘‘They were all [in] very good condition, but not the detainees.

‘‘These are, after all, not people who are criminals and so they were handling the detention badly; many attempts at self-harm, and I’m still receiving reports of self-harm, suicide attempts and protests at the off-shore processing facilities. And these are all highly worrying - and unfortunately it was a predictable outcome.’’

Ms Pillay said that combating people smugglers was important to protect people’s rights and praised regional talks.

‘‘But I must stress that these should be underpinned by strong legal protections in line with the government’s human rights obligations.’’ – The Age