HOI AN, Vietnam - Typhoon Ketsana extended its destructive rampage through Southeast Asia Wednesday, blowing away whole villages in Vietnam, Cambodia and Laos as the regional death toll rose to 312.

The storm has unleashed some of the worst flooding in a decade and left governments in the disaster-prone region struggling to help more than two million people who are either homeless or in urgent need of supplies.

"I have never seen such a strong wind in my life," Pang Phot, a police officer in Cambodia's badly-hit Sandann district, told Agence France-Presse by telephone.

"Many wooden houses were immediately blown away and many others collapsed to the ground. It was raining heavily and people could not flee their homes because the wind hit immediately," he said.

Landslides buried homes and rising waters threatened ancient world heritage sites as the storm finally moved inland towards Laos and weakened to a tropical depression Wednesday.

Ketsana killed 246 people in the Philippines over the weekend while still a weaker tropical storm, before strengthening into a typhoon over the South China Sea and smashing into central Vietnam on Tuesday, leaving another 55 dead.

It moved inland to lash Cambodia overnight, killing 11 more people, and caused meter-high flooding in Laos on Wednesday. Authorities in northeastern Thailand were also on high alert but said there had been no damage yet.

Vietnam's flood and storm control committee listed 11 missing in addition to the 55 confirmed dead. The toll included 13 in mountainous, inland Kon Tum province and 14 in central Quang Ngai province where the typhoon made landfall.

The Vietnamese town of Hoi An, a UNESCO world heritage site, was under three metres (10 feet) of water, Agence France-Presse journalists said. The town is a major tourist draw for its centuries-old pastel-coloured buildings.

"This flooding might be bigger than the historic floods in 1999," said Nguyen Su, the Communist Party chief in Hoi An.

On Tuesday flooding hit parts of Danang as well as Hue, the former capital and another World Heritage site, where residents used small wooden and steel boats to move around.

The flood and storm control committee said that six coastal provinces had been evacuated, involving 168,585 people. Many areas were without power.

Deputy Prime Minister Hoang Trung Hai said military helicopters could be sent to join the rescue effort, adding that they would immediately evacuate households on river banks and areas likely to suffer from landslides.

In Cambodia, authorities said the homes of thousands of people had been evacuated as the storm packed winds of up to 145 kilometres (90 miles) an hour.

Nine were killed and 28 injured in central Cambodia while two died in the northeast overnight as the country was battered by the storm, officials said. The victims included a grandmother, mother and three children in one house.

"At least nine people were crushed last night when their houses fell down," said Chea Cheat, chief of the Red Cross office in central Kampong Thom province, adding that at least 92 houses in his province were destroyed.

In deeply impoverished and isolated Laos, five or six villages had reportedly been flooded in Savannakhet province and aid workers were making their way there by car, aid agency World Vision said.

"We have the capability to urgently ready 500 aid packs if our assessment teams find these are needed," World Vision aid worker Vatthanathavone Inthirath said.

In the Philippines, the United States said Wednesday it would send soldiers and military equipment to help its former colony recover from devastating floods triggered by Ketsana.

Ketsana dumped the heaviest rains in more than four decades on Manila and surrounding areas on Saturday, submerging 80 percent of the nation's capital.

Four days later, some areas remained underwater or knee-deep in mud, while hundreds of thousands of people were crammed into makeshift evacuation centres.

Meanwhile there were warnings that another looming typhoon may add to the devastation. Typhoon Parma was lurking to the east of the Philippines and on course to hit the country on Thursday or Friday.