Local immigration police officer Pham Van Truong said a total of two British tourists, a Frenchman and a local guide died in the accident on Thursday and that a Vietnamese tourist was still missing.

"There was very heavy rain at the time of the accident," he said.

A French tourist on the boat said there were 31 people on board, including South Africans, Japanese and Australians, as well as the Britons and Frenchman who died. Police had earlier said there were 32 on board.

Halong Bay, located in the Gulf of Tonkin about 160 kilometres (100 miles) east of the capital Hanoi, was declared a UNESCO World Heritage site in 1994.

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

Numerous tourist boats that ply the waters of the bay offer sleeping and dining facilities.

Last year 2.65 million tourists, including 1.71 million foreigners, visited Halong Bay, according to the provincial tourism department.

Agence France Presse - September 29, 2009