(CNN) -- At least 12 people died when a tour boat on Vietnam's Ha Long Bay sank early Thursday, an official said.
The dead included 10 foreigners -- two from the United States; one from the United Kingdom; two from Russia; one from Japan; one from France; two from Sweden; and one from Switzerland, said Nguyen Van Chieu, director of the foreign relations department for Quang Ninh province.
Those who died were asleep in their cabins and were trapped there, he said.
Personnel from the embassies have arrived at the hospital, he said, and officials are "waiting for decisions from embassies whether to repatriate them to their home countries," Chieu said.
The bodies had been taken to a local hospital for identification, said Ngo Van Hung, director of the Ha Long Bay managing board. One of the Vietnamese was the tour guide. The other was an Australian of Vietnamese origin, Chieu said.
Fifteen people, including nine foreigners, were rescued following the incident, according to Do Thong, vice president of Quang Ninh province. One of those rescued was American, said Chieu.
"We can confirm that there were three American citizens on board, two of whom are deceased," U.S. State Department Acting Deputy Spokesman Mark Toner told reporters Thursday.
Authorities believe the wooden vessel sank when a plank on the boat ripped away and are investigating the incident.
The water at the site was about 4 meters (13 feet) deep. A witness said the boat was listing Wednesday night, Chieu said. It turned vertical and sank within a few minutes early Thursday.
"We have not pulled up the boat yet, so I can't say anything about the cause" of the sinking, Chieu said. He said the boat was anchored in safe water and there were about 40 other boats in the area at the time.
Ha Long Bay is about 165 kilometers (102 miles) east of the Vietnamese capital, Hanoi. It is a frequent tourist destination, known for thousands of limestone mountains jutting up from the water.
CNN's Brittani Saylor and Journalist Hau Dinh contributed to this report.