A group of 49 Vietnamese citizens held at the Port Augusta community immigration facility in South Australia have been told they have no right to stay.

The group includes 44 unaccompanied minors, among them a six-year-old who a source with knowledge of the detainees says may be in the company of an older sibling.

Refugee groups say the decision raises questions about the future of unaccompanied minors being processed at Christmas Island for transfer to Malaysia.

A department spokesman said talks with Vietnamese authorities about organising the group's return were under way.

"None of these clients raised any claims for protection and the majority stated they came to Australia to work or study," the spokesman said. "Immediate post-return assistance is available for all clients, including minors, who are being returned."

Greens immigration spokeswoman Sarah Hanson-Young said an explanation was needed from Immigration Minister Chris Bowen.

"There is no question that the Migration Act is very clear that the minister is the legal guardian of any child that arrives in Australia unaccompanied . . . no matter what country they are from," Senator Hanson-Young said.

"There are very serious questions that need to be answered as to whether the minister is upholding his obligations as defined under the act."

Mr Bowen said he was complying with international law.

"The government ensures appropriate arrangements are in place to ensure the safe return of unaccompanied minors, with their needs taken into account," he said.

"We take our obligations under international law seriously and will not return a person in breach of those obligations."

All had arrived by boat and been processed at Christmas Island, and it is understood most if not all were transferred to Port Augusta in June.

Ian Rintoul from the Refugee Action Coalition criticised the government, saying if unaccompanied minors were sent back to Vietnam then it was likely that other minors on Christmas Island would be sent to Malaysia.

"The minister is the guardian for the Vietnamese unaccompanied minors in Port Augusta as much as he's the guardian for the people on Christmas Island," Mr Rintoul said.

"If the minister was seriously putting the rights of the child and the welfare of the child (first) . . . he wouldn't be sending unaccompanied minors back to the streets of Vietnam or Kuala Lumpur."

By Mark Schliebs - The Australian - August 6, 2011