Divers worked to winch a sunken tour boat out of Vietnam's picturesque Ha Long Bay on Friday, a day after 12 sleeping travelers from nine countries drowned when the vessel suddenly filled with water while anchored for the night.

Divers bobbed in the calm, frigid water while trying to attach cables to the ship, which was submerged about 30 feet (10 meters) below the surface. The Bien Mo, or Dream of the Ocean, went down before dawn Thursday, killing vacationers from the U.S., Britain, Australia, Japan, Russia, France, Sweden and Switzerland along with their Vietnamese tour guide.

It was Vietnam's deadliest tour boat accident since opening up to foreign visitors 25 years ago.

Most of the travelers were sleeping in the traditional wooden boat's cabins when it rapidly began taking on water. Nine foreigners and six locals survived only by flinging themselves overboard and swimming to other tour boats nearby. Others were trapped inside.

Some passengers had questioned the boat's safety the night before the disaster after feeling it lurch to the right side.

"The boat was sinking, was bending," survivor Stefano Corda, 35, of Palermo, Italy told Associated Press Television News, recalling the feeling that something was wrong while eating dinner about 10 p.m. "We said to the crew, 'What happened to the boat?' But they replied it was normal."

Friday's Transport newspaper, published by the government, reported that the boat was put into operation in November 2008 and licensed to provide overnight services. The 94-foot (29-meter) -long, 23-foot (7-meter) -wide vessel was equipped to carry 30 passengers, including 20 people in its 10 cabins. It passed its last safety check four months ago.

Ha Long Bay is one of Vietnam's top tourist attractions. Some 2.5 million visitors, about half foreigners, cruise the bay each year to take in its spectacular 1,600 jagged rock formations jutting out of the water to form tiny islands near the Chinese border. Many opt for cheap day trips, while others choose to stay on one of the some 120 boats offering overnight accommodation, ranging from budget to luxury.

Police are investigating what caused Thursday's accident, and the boat captain and crew have been summoned for questioning, said Le Thanh Binh, a Quang Ninh police spokesman.

Survivors reported seeing a wooden plank ripping away from the ship around 5 a.m., followed by gushing water inundating the cabins and quickly pulling it under near Titov island, about an hour from the mainland.

"We woke up at 5, and the boat took one minute to sink," Corda said. "We went to the exit and the boat was almost vertical. I grabbed my friend, we went out, and it was so fast."

Corda's friend, Stefano Sacconi, 33, of Rome, was in the bathroom just before the disaster struck. He thought he felt the boat buckling on its right side and soon realized they needed to get out. And fast.

"We started to hear tables and glasses falling from the top of the restaurant," he said. "After that, my friend went out. He called me, 'Come up! Come up! Something's wrong here! The boat is going down!'"

They jumped and swam to another nearby ship.

Friday's Tuoi Tre newspaper quoted survivor Nguyen Khuong Duy, a Vietnamese-Australian, as saying that it happened so fast, only crew members and passengers on the upper deck had time to jump. Those on the lower deck were simply swallowed.

There were 27 people, including six crew members, aboard the boat and all have been accounted for, said Vu Van Thin, chief administrator of Quang Ninh province. The vessel, which is owned by Truong Hai Co., was anchored alongside dozens of other cruise boats and weather conditions were calm at the time of the sinking. Thin said the tour company's two remaining cruise boats have been docked during the investigation.

The official Vietnam News Agency published the victims' names and ages, most of them aged 20 to 25, seven were women. They include a Briton, two Americans, one Japanese, one French, two Swedes, two Russians, one Swiss and one person of Vietnamese origin living in Australia, according to the government.

One American was Samantha Kay Taylor, a recent graduate of the University of Colorado at Boulder, who was overseas teaching in China and traveling.

Her boyfriend, George Fosmire, 23, a University of Colorado at Boulder student, was traveling with her, and after the accident, went to the morgue to help identify the bodies of his girlfriend and their good friend, said Fosmire's father, William Fosmire of Golden, Colorodo, in an Associated Press interview.

"This is a very rare and very unfortunate accident," said Foreign Ministry spokeswoman Nguyen Phuong Nga. She said tour companies should improve safety measures in Ha Long Bay.

Vietnam's foreign ministry confirmed the survivors as two Danes, one German, two Italians, one American, one Australian, one French and one Swiss.

Ha Long Bay is a U.N. World Heritage in the Gulf of Tonkin about three hours east of the capital, Hanoi. The bay has had at least three fatal boat sinkings in the previous decade. Storms or windy conditions were blamed for sinkings in 2009, 2006 and 2002, which killed at least a dozen people in all.

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Associated Press writers Tran Van Minh and Margie Mason contributed to this report from Hanoi, Vietnam, and Sheila V Kumar contributed from Denver.