Image caption Those rescued have begun arriving at Christmas Island

Rescuers are continuing to search for dozens of people believed to be missing after a boat sank near Christmas Island, off north-western Australia.

Ships have so far picked 109 survivors from the sea, but officials believe about 200 people were on the boat.

Three bodies have been recovered and an Australian minister said more bodies had been seen in the water.

The ship, believed to be carrying asylum-seekers, capsized on Thursday.

Christmas Island is closer to Indonesia than Australia, and is targeted by asylum-seekers hoping to get to Australia, often on boats that are over-loaded and poorly maintained.

Australian patrol vessels, merchant ships and aircraft have been helping with the rescue.

Christmas Island

The Australian government earlier put the number of survivors at 110 but then revised this down to 109. One of those rescued was a 13-year-old boy and everyone on board the boat was said to be male.

A navy boat has brought the survivors to Christmas Island, where Australia has a large immigration detention centre. They are said to be undergoing medical checks there, with three taken to hospital.

Australia's Home Affairs Minister Jason Clare has told local media that most of the men were from Afghanistan.

He also said that a surveillance plane has spotted more bodies in the water, but no more survivors so far.

"Unfortunately, I can't report that any more survivors were seen alive in the water at this time," he told local media.

"We need to brace ourselves for more bad news. Potentially, many more people have lost their lives."

'Hazardous journeys'

Officials said the boat issued an emergency call and was later found to be in distress by an Australian surveillance plane.

About 40 people were found clinging to the hull of the boat and more were found holding on to debris, Mr Clare said.

A spokeswoman from Australia's Maritime Safety Authority (AMSA) said water temperatures were fair, which made finding survivors more likely.

In recent years a flow of asylum-seekers, mainly from Afghanistan, Sri Lanka and Iraq, have been making their way to Australian territory by boat via Indonesia.

There have been a number of capsizes blamed on unseaworthy vessels carrying too many passengers.

About 50 asylum-seekers died when their boat broke up on rocks off Christmas Island in December 2010.

"This accident again underscores the dangerous nature of these hazardous journeys, and the desperate and dangerous measures people will resort to when they are fleeing persecution in their home countries," the UN refugee agency said in a statement.