Halong City (Agencies): Twelve people, most of them foreign tourists, died on Thursday when their tour boat suddenly sank while they slept in Halong Bay, one of Vietnam's top tourist spots, officials said.

The 12 dead included 10 foreigners and two Vietnamese, informed Vu Van Thin, a local government official in Quang Ninh province.

Immigration police in the province remarked the foreign victims were believed to comprise two Americans, two Russians, two Swedes, and one each from Britain, Japan, France and Switzerland.

Sweden affirmed that two of its citizens, both women in their early 20s, had died in the tragedy.

France's embassy in Hanoi confirmed that French people were "involved" in the incident, but their situation was not yet clear.

Vu Van Thin said the Vietnamese victims included a tourist and an interpreter for the overseas visitors.

Nine tourists and six crews survived the tragedy, he said.

Many Halong Bay tour boats have dining facilities and cabins for tourists, seeking relaxation, to spend the night on the waters.

"According to our initial information part of the boat suddenly broke," but bad weather was not to blame, said Thin.

Halong Bay, situated in the Gulf of Tonkin about 160 kilometres east of the capital Hanoi, was declared a UNESCO World Heritage site in 1994.

Its 1,600 islands and islets form a beautiful seascape of mostly uninhabited limestone pillars made famous by the 1992 French movie "Indochine".