SINGAPORE— Singapore's port authority says rescuers are searching for 11 missing crewmen after a tugboat sank off the coast of the city-state.

The Maritime and Port Authority says the Singapore-registered Ocean Lark went down early Wednesday off Pedra Branca island, 34 miles (54 kilometers) east of the city.

It says two of the boat's 13 crew members were rescued by another ship and the air force and navy are searching for the other 11.

The port authority did not immediately say why the boat sank. (AP)