Twenty-seven fishermen are missing after a Vietnam-registered vessel sank in the South China Sea, said maritime rescue authorities Thursday.

The fishing vessel, named "PHU TAN", capsized and sank due to strong gales in the seas about 110 nautical miles to the west of Sanya City in the southern island province of Hainan, said a spokesman with the South China Sea Salvage Bureau.

Twenty-seven fishermen fell overboard into the water, said the spokesman.

The salvage bureau immediately dispatched a rescue vessel to search for the missing after it received two emergency calls from the Vietnamese maritime department at noon.

Hindered by gales of up to 90 km per hour, the rescue vessel was expected to reach the site where the fishing vessel sank by 9 p.m.

A towboat travelling about 40 sea miles away from the site was ordered to assist with the rescue.