At least 11 tourists and a guide have drowned after a tour boat sank in Halong Bay in northeastern Vietnam.

The boat was touring in the picturesque Unesco World Heritage Site in Quang Ninh province when it went down.

At least 21 foreign tourists were on the live-aboard boat when it sank before dawn near Titov island.

Vietnamese media quoted a provincial vice-governor as saying the tourists on board were from the US, the UK, France, Russia, Denmark and Sweden.

"So far the rescue team has rescued 15 people, including nine foreign tourists and six crew, and pulled out 12 bodies," Ngo Van Hung, director of the Halong Bay Management Department, told Reuters by telephone.

All of the bodies have been sent to Bai Chay Hospital for identification.

A hospital manager said the survivors were "in panic" but had now returned to their hotels.

Vu Van Thin, a senior official with the Quang Ninh province People's Committee, the local government told reporters that bad weather did not cause the sinking.

"According to our initial information part of the boat suddenly broke," he said.

The boat carried two Vietnamese tourists, one of whom is believed to have died.

Halong Bay, whose name translates as "Descending Dragon Bay", is renowned for its limestone karsts and isles.

Tourists often stay overnight on boats touring the hundreds of islets scattered throughout the scenic bay.

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