It was the country's deadliest tour boat accident since opening up to foreign visitors 25 years ago.
The local port authority said Friday that all overnight tour operations on the bay had temporarily been suspended. Day cruises were not affected.
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 by flinging themselves overboard and swimming to other tour boats nearby. The others were trapped inside.
Some passengers had questioned the boat's safety the night before after feeling it lurch to the right side.
"The boat was sinking, was bending," survivor Stefano Corda, 35, of Palermo, Italy, said, 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."
It was too early to tell whether the tilting feeling was linked to the sinking.
One potential cause could have been the boat's wooden planks drying out, creating cracks for water to seep inside, said Le Van Cach, director of Tan Phuc maritime rescue company, who was at the scene.
"It could be one of the reasons for a wooden boat to sink in normal weather conditions," he said. "The damage is still underwater at the moment, and I can't confirm anything."
Friday's Transport newspaper, published by the government, reported that the boat was put into operation in November 2008. 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. Many opt for cheap day trips, while others stay on one of the 120 boats offering overnight accommodation, ranging from budget to luxury.
Hundreds of tourists lined up on the port's main dock Friday morning to take day cruises, undeterred by the disaster.
"We have a good tourist company that we travel with, and they assure us that the boat will be safe," said Dale Daniels, 59, of New Jersey. She had planned an overnight trip, but it was canceled. Police are investigating what caused Thursday's accident, and the captain and crew of the vessel, owned by Truong Hai Co., 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.
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.
On Friday, a twisted mess emerged with the wreckage, telling an eerie story of a dream holiday suddenly turned tragic.
Floating rattan chairs and tables along with soda cans bobbed inside the vessel as it was lifted. The cabins' windows were smashed, and the curtains ripped away and tangled with bed sheets and pillows.
Crews planned to drag the boat to a nearby island and pump the water out of it before pulling it back to the mainland.
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 female Swedish childhood friends, a Russian mother and daughter, one Swiss and a Vietnamese man who is a permanent Australian resident, according to the government and embassies.
"We are devastated," said Bryan McCormick, father of British victim Stuart McCormick, 30, who was on a yearlong round-the-world adventure. "We had a couple of e-mails from him from Vietnam, and he was having a great time and enjoying himself."
Vietnam's foreign ministry confirmed the survivors as two Danes, one German, two Italians, one American, one Australian, one French and one Swiss.
Associated Press writers Tran Van Minh and Margie Mason in Hanoi, Vietnam, Louise Nordstrom in Stockholm, Sweden, and videographer Yves Dam Van in Ha Long Bay contributed to this report.