Heavy rains that began late last week have washed over three provinces, Nghe An, Quang Binh, and Ha Tinh -- where a state of emergency was declared on Tuesday afternoon.

Police in Ha Tinh said the bus disappeared on Monday in flood waters on the main north-south Highway 1A.

Hundreds of soldiers using boats and metal detectors were mobilised to search for the missing passengers, state television reported.

"I think they are all dead," Tran Van Long, deputy head of police in Nghi Xuan district, told AFP.

"The search will continue until the time we find the bus and the bodies."

He said relatives of the 18 missing converged on the scene beside the swollen Lam River, near Vinh city, where rain had stopped and the waters were gradually receding.

VietnamNet online news site listed the names of the 18, who included 11 women and three children, among them an eight-month-old girl.

A survivor, Tran Dac Luc, 57, of Dak Nong province, was quoted by VnExpress news site as saying the bus floated at first, but then began to sink slowly as the driver tried to calm passengers' frightened shouts.

"The driver asked everyone to stay calm so that he could try to drive onto the pavement," Luc reportedly said. When that did not work he asked people to break the windows, which would not open until he used a wrench, allowing several people to crawl out, he said.

Luc escaped only to watch his son and niece climb free but retreat to the bus because they could not swim, VnExpress quoted the weeping man as saying.

"We looked at the bus sinking completely," he said. After diving into the water in a failed rescue attempt, Luc gave up and swam towards other survivors clinging onto cables. "I have no hope for them to be alive. My only comfort would be to find their bodies to bring back home for burial," he was quoted as saying.

Local media said the bus driver was one of 18 people who survived.

The floods have wreaked havoc in Ha Tinh and the two adjacent provinces, where authorities said more than 150,000 homes had been inundated.

"The disaster has left thousands of people in the province penniless after their assets were swept away in the flood waters," the chairman of Ha Tinh's local government, Vo Kim Cu, was quoted as saying in the state Vietnam News on Tuesday. Later he told the official Voice of Vietnam radio that residents should be prepared for more rains and flash floods. Television pictures showed rescuers in boats delivering instant noodles.

"My house is flooded to the roof," Nguyen Thi Mai, a Ha Tinh resident, said on national radio.

She said all her furniture had floated away but she and her husband were staying.

"Officials gave us noodles and clean water today."

People have suffered "a very severe shortage of food products" in recent days and the top priority is to get them food and water, Nguyen Bang Toan, a Communist Party district chief in Ha Tinh, said on state television.

"We have to save them from hunger," he said.

The international Red Cross on Monday appealed for more than one million dollars in aid for victims of the flooding, the second major inundation to hit the central region this month.

Earlier floods left at least 64 people dead in Quang Binh and other central provinces.

Agence France Presse - October 19, 2010