Coast guards are working to recover three passengers trapped under the capsized hull of a tour boat which capisized off the coast of Turkey's southwestern province of Mugla today, an official said.

The boat, named Anemore, was carrying 11 people when it sank off the Marmaris district of Mugla, a popular tourist area, the official said. Eight passengers have so far been rescued.

"The ship sank rapidly for an unknown reason about 500 metres from the Marmaris-Bozburun gulf," the official said.

The cause of the accident was not immediately clear, the official said, adding that emergency services were searching for the three missing people, who include the boat's owner.