Typhoon Xangsane barrelled into central Vietnam Sunday, forcing tens of thousands to flee and cutting electricity and many telephone lines after killing scores of people in the Philippines.
Six people died and 51 people were injured in four provinces, according to the first reports released by the Vietnamese rescue operation.
Strong winds uprooted trees and destroyed roofs in the central city of Danang, where the Han River broke its banks, an AFP journalist witnessed.
Air and train travel across the country was disrupted.
Authorities evacuated at least 180,000 people Saturday ahead of the storm, which was expected to dump heavy rains on several heavily-populated areas of central Vietnam, including the region's popular tourist beach resorts.
"I think this will be one of the biggest storms to hit Vietnam in the past few decades," Le Huy Ngo, head of the steering committee on flood and storm control, told AFP at the rescue center in Danang.
"Apart from coping with the storm, we will have to deal with flash floods and landslides."
Xangsane -- which was packing maximum sustained winds of 148 kilometers (90 miles) an hour early Sunday, according to the Hong Kong observatory -- has already claimed the lives of at least 76 people in the Philippines.
Millions were still without power and clean drinking water in the Philippines capital Manila and the surrounding area, officials said Sunday. Sixty-nine people were still reported missing.
In Vietnam, rescuers, coast guards and the military were struggling to avoid a repeat of the devastation wrought by Typhoon Chanchu in May, which left 267 people dead or missing -- a toll blamed on the failure of the storm response system.
By mid-day, many electricity and telephone lines were cut in the four provinces heavily hit by the epicenter of the typhoon, namely Danang, Thua Thien-Hue, Quang Nam and Quang Ngai.
Five other provinces have also been badly affected by strong winds and rains.
Deputy Prime Minister Nguyen Sinh Hung and Agriculture Minister Cao Duc Phat had initially planned to visit the worst affected areas on Sunday.
But their plan could be made difficult as many roads were flooded and barred by broken trees, officials said.
Helicopters were ready to take off but were grounded by the wind, state television noted.
The popular tourism resort town of Hoi An, where at least 450 foreigners were evacuated Saturday, was also badly flooded.
The former royal capital of Hue was said to be in "serious" situation with the local Huong River rising dangerously, but the ancient citadel might not suffer too much, local officials said.
In Danang, where roughly 800,000 people live, police "ordered a ban on travelling in the whole city," said Colonel Nguyen Dinh Chinh, deputy director of Danang Police.
Losses "will be big as Danang city faces the sea," said Van Phu Chinh, head of the Danang-based central region's committee on flood and storm control.
"In 1988, Danang suffered a similar devastating storm, killing 94 people. But at that time, the power of the storm and the wind were not that bad," he added.
Several neighbouring countries permitted Vietnamese fishermen to seek shelter following a request by the Vietnamese authorities, said Deputy Prime Minister Hung.
Nguyen Ngoc Quang, head of the Quang Nam committee on flood and storm control, said Sunday around 4,000 inhabitants on the province's seven islets of Cu Lao Cham had lost all contact with the mainland.
State media said the weakened typhoon would later hit Laos later in the day.