There are grave fears for as many as 20 asylum seekers believed to have drowned after their boat sank in the early hours of Tuesday morning while en-route to Australia.

At least seven people were confirmed dead late on Tuesday by Indonesian authorities, who said the boat went down just hours after leaving from a port in Central Java.

The death toll was expected to rise with more people still missing.

Two young boys and three women were among those confirmed dead by authorities.

The boat, which left from Cilacap in Central Java with a crew of three, was carrying about 70 asylum seekers who had arrived in Indonesia from the Middle East.