Rescuers have safely pulled six people from the waters off Indonesia, but are still searching for many more after a boat carrying asylum seekers sank.

A merchant ship rescued the six survivors early Thursday, about 75 kilometers southwest of Java, after they had spent almost a day in the water.

Indonesian ships, along with an Australian naval vessel and aircraft are searching the area for more than 140 people who remain missing. Australian Home Affairs Minister Jason Clare says there are “grave concerns” for those yet to be found.

Australian authorities received a distress call Wednesday saying the boat was having engine problems.

Asylum seekers frequently attempt the dangerous trip from Indonesia to Australia's Christmas Island, often with the aid of smugglers.

Officials say nearly 1,000 people have died trying to reach Australia by boat since 2001.

Australia recently passed new laws to try and deter such trips by setting up offshore processing camps for asylum seekers.

Right groups criticize the plan, saying it is a major setback for Australian refugee policy.