Jakarta - A Pakistani and two Afghan refugees were killed after a boat carrying 18 Australia-bound foreign asylum seekers who escaped an Indonesian immigration detention centre sank off eastern Indonesia, police said Thursday.

Nine people survived after the boat capsized in the Pakuafu Strait off Rote island in East Nusa Tenggara province on Wednesday, said provincial police spokesman Octo Riwu.

Six other asylum seekers and three members of the boat's crew remained missing, he said.

The 18 foreign nationals from Afghanistan, Pakistan and Myanmar escaped from the immigration detention centre in the provincial capital Kupang Wednesday after overpowering guards and fled in a car which appeared to have been waiting for them, police said.

"We are investigating the possible involvement of a local people-smuggling ring in the escape," Riwu said by telephone.

"We are still unable to question the survivors because they are still sick," he said.

The escapees were among 33 foreigners arrested late last year for entering Indonesia illegally on the way to Australia.

Indonesia has long been used as a transit point for foreigners seeking asylum in Australia. (dpa)