Super Typhoon Yagi hit island districts of north Vietnam about 1300 local time (0600 GMT) on Saturday, generating winds of up to 160km/h near its centre, having lost power from its peak of 234km/h in Hainan on Friday.
A body was recovered near the coastal city of Halong, while a dozen people were missing at sea, state media reported on Saturday.
Super Typhoon Yagi has made landfall in northern Vietnam after tearing through southern China. (AP PHOTO)
Earlier in the day, a 53-year-old motorcyclist was killed after a tree fell on him in the northern Hai Duong province, state media reported.
Yagi had already claimed the lives of at least 16 people in the Philippines, the first country it hit, having formed east of the archipelago earlier in the week.
Vietnam's coastal city of Haiphong, an industrial hub with a population of two million people that hosts factories from foreign multinationals and local car maker VinFast, was among the hardest hit by winds with speeds of up to 90km/h.
As the typhoon approached, the city experienced power outages on Saturday, authorities said.
The strong winds smashed windows in buildings and waves were as high as three metres when they hit the coast, according to a Reuters witness.
Trees fell and metal roofing sheets flew away from buildings and parking lots, pictures and footage on local media showed.
Authorities in Vietnam evacuated almost 50,000 people ahead of Yagi's arrival. (AP PHOTO)
Earlier in Hainan, which has a population of more than 10 million, the storm felled trees, flooded roads and cut power to more than 800,000 homes.
Vietnam evacuated almost 50,000 people from coastal towns and deployed 450,000 military personnel, the government said.
It also suspended operations for several hours at four airports on Saturday, including Hanoi's Noi Bai, the busiest in the north, cancelling more than 300 flights.
High schools were also closed in 12 northern provinces, including in the capital Hanoi, which has a population of 8.5 million.
Authorities in the capital suspended public transport on buses and its two elevated metro lines on Saturday afternoon, state media reported.
The clean-up has begun in southern China after Yagi felled trees, flooded roads and cut power. (AP PHOTO)
The meteorological agency has warned of risks of heavy flooding in the city centre.
"The wind is strong enough to blow a person over," Hanoi resident Nguyen Manh Quan, 40, said.
Dang Van Phuong, also 40, said: "I've never seen a storm like this, you can't drive in these winds."
Typhoons are becoming stronger, fuelled by warmer oceans, amid climate change, scientists say.
Typhoon Shanshan slammed into southwest Japan at the end of August - the strongest storm to hit the country in decades.
Yagi is named after the Japanese word for goat and the constellation of Capricornus.
