Refugee advocates want the Federal Government to move an 11-year-old asylum seeker out of detention at Pontville near Hobart, and into the local community.

The Pontville centre, re-branded as an alternative place of detention by the Immigration Department, has been used to detain almost 300 unaccompanied minors from places like Afghanistan, Vietnam, Iran and Sri Lanka.

The Sri Lankan child is being held along with two older cousins, but the Immigration Department will not say how long they have been held.

Psychiatrist and asylum seeker advocate Professor Louise Newman says the children need to be moved.

She says there are serious mental health risks for children in detention.

"We start to see children showing quite clear signs of trauma," she told AM.

"Some children becoming very child-like, if you like - regressing to an earlier developmental stage. Others starting to feel angry and frustrated."

Professor Newman says children are not in a position to understand the situation they are in.

She says it is much more appropriate for those children to be placed in foster families.

"I think most people would not want to see children who are young in an environment where they're likely to be feeling frightened," she said.

The Department of Immigration says it is focused on keeping the extended family together, but says it cannot say when the Sri Lankan children will be moved out of the centre.

The ABC's attempts to contact new Immigration Minister Tony Burke have so far been unsuccessful.

Mr Burke visited the Pontville facility on Friday, and declared he did not want any young person permanently held in detention.

He has since approved the release of 18 young Pontville detainees, who will be released into community detention around the country.

Almost 800 unaccompanied minors are seeking asylum in Australia and 335 of those children are having their claims assessed in the community. (Source: abc.net)