More than two dozen crew members are unaccounted for after their ship broke into two during a typhoon in the South China Sea on Saturday, with rescuers scrambling to find them, officials say.

An engineering vessel that was 160 nautical miles southwest of Hong Kong "suffered substantial damage and broke into two pieces" and the 30-member crew abandoned ship, according to the Hong Kong Government Flying Service.

Three people had been rescued as of 3:00pm local time (0700 GMT) and were taken to hospital for treatment, authorities said.

Dramatic footage provided by Hong Kong authorities showed a person being airlifted onto a helicopter while waves crashed over the deck of the semi-submerged ship below.

The three survivors said other crew members may have been swept away by waves before the first helicopter arrived, according to a government statement.

Typhoon Chaba earlier formed in the central part of the South China Sea and on Saturday afternoon made landfall in Guangdong province in southern China.

Rescuers in Hong Kong were notified of the incident at 7:25am local time (2325 GMT on Friday) and found the ship near Chaba's centre, where harsh weather conditions and nearby wind farms made the operation "more difficult and dangerous".

The ship's location recorded wind speeds of 144 kilometres per hour and waves that were 10 metres high, authorities said.

The Government Flying Service dispatched two sorties of fixed-wing aircraft and four helicopter sorties, with mainland Chinese authorities also dispatching a rescue boat.

Rescuers said they would increase the search area "due to the large number of people missing" and extend the operation into the night if conditions allowed.