Asylum boat search on hold overnight

Authorities have scaled back a search-and-rescue mission for survivors of an asylum-seeker boat that sank in the Sunda Strait.

Searchers have found 55 survivors so far from an asylum-seeker boat that sank near Indonesia.

The wooden boat was carrying an estimated 150 people and hopes are fading for those who have not yet been located.

Two distress signals were received from the boat early on Wednesday morning off Java's western-most tip but a search failed to find them.

However, early on Thursday morning, a merchant vessel acting on information from the Australian Maritime Safety Authority (AMSA) found six survivors 45 nautical miles from Indonesia, sparking a major search operation.

AMSA said at 2200 (AEST) on Thursday the search-and-rescue operation by Indonesian authority BASARNAS and Rescue Coordination Centre (RCC) Australia would be scaled back overnight and resume at first light on Friday.

"Vessels will remain on the scene overnight, but have limited search capability until daylight," AMSA said in a statement.

At that time, 55 survivors had been recovered.

Three of them had serious injuries but were in a stable condition on board HMAS Maitland.