SYDNEY, New South Wales (AFP) - An asylum-seeker boat heading for Australia has sunk off Java in Indonesia with unconfirmed reports on Wednesday that up to 60 people are dead or missing.

The Australian Maritime Safety Authority (AMSA) confirmed to AFP that a rescue operation was underway, but said it was being coordinated by Indonesian authorities.

"We are aware of an incident south of Java. Indonesian authorities are responding. Australian authorities are not involved in the incident," an AMSA spokesman said.

Reports in Australia said the boat carrying more than 170 people, mostly from Sri Lanka and Iran, broke up and sunk in heavy seas on Tuesday evening.

The Sydney Daily Telegraph, reporting from Java, said around 60 people were dead or missing after the engine of the boat started smoking and taking on water shortly after departure.

"I am the only one back," a man named Soheil told the newspaper about the group of 61 Iranians he was travelling with, who set of from the fishing village of Cidaun.

Other reports said only one person, a child, was so far confirmed dead.