A boat carrying about 200 suspected asylum seekers has capsized in Indonesian waters 120 nautical miles (220 km) north of Australia's Christmas Island, rescue officials said on Thursday.

An Australian customs spokesman said border protection had detected what was believed to be a people-smuggling boat in distress earlier on Thursday.

The sinking occurred within Indonesia's search and rescue zone and Australian authorities were offering assistance, Australia's Maritime Safety Authority said.

An Australian defence force aircraft had spotted survivors in the water, Sky News reported.

Refugees seeking asylum in Australia often set sail from Indonesia heading for Christmas Island in dangerous and overcrowded boats.

Fifty asylum seekers travelling from Indonesia to Christmas Island died when a storm dashed their boat onto rocks in December 2010.  - Reuters