Twelve Chinese sailors have died and nine others are critically ill after a suspected case of food poisoning on board their vessel near Vietnam's southern Con Dao island, a rescue official and state media said Friday.

The Chinese-registered Wu Zhou 8 cargo vessel was on its way from Thailand to China when the 21 crew members fell ill, state media reported.

"We were told of 10 bodies on the vessel. All died because of food poisoning, we were told," an official involved in the rescue effort told AFP from Vietnam's southern Ba Ria Vung Tau province.

The cause of death was yet to be confirmed, he added.

"We have sent our rescue ship, which is scheduled to reach the Chinese vessel late Friday night," said the official, who declined to be named.

Eleven other sailors were brought to hospital in an aircraft hired by the vessel's owner. Two died on the way, while nine are being cared for by Vietnamese medics on land.

State media said the Chinese vessel is now 63 nautical miles from Con Dao island.

On Thursday, seven bodies were found floating off Vietnam's southern Phu Quoc island.

They were believed to be from a boat that sank off Cambodia's coast last week with 41 Chinese people on board.