Seven people had already been rescued, said a fire services commander, Mr Wong Chung-shing, who declined to speculate if the missing crew were still alive.

But he said divers had knocked on the hull and got no response, RTHK reported.

The missing were thought to be trapped in the engine room and cabins of a tug which collided with a cargo ship on Saturday night and was now on the seabed at a depth of 35 metres, Mr Wong said.

It took divers four hours to locate the sunken vessel, which was found 400 metres from the location initally given by maritime police, probably because it was moved by a strong current, he said. -- AFP