At least another dozen were missing at sea in Vietna, according to state media.
Asia's most powerful storm this year made landfall in northern Vietnam on Saturday, the meteorological agency said, killing at least four people after tearing through China's island of Hainan and the Philippines.
Super Typhoon Yagi hit island districts of north Vietnam around 1 p.m. (0600 GMT), generating winds of up to 160 kph (99 mph) near its centre, having lost power from its peak of 234 kph (145 mph) in Hainan a day earlier.
The government said that as of 5 p.m. four people had died and 78 had been injured by the typhoon. At least another dozen were missing at sea, according to state media.
Yagi had already claimed the lives of at least two people in Hainan and 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 2 million people that hosts factories from foreign multinationals and local carmaker VinFast, was among the hardest-hit by winds with speeds of up to 90 kph.
As the typhoon approached, the city experienced widespread power outages on Saturday, authorities said, as did at least three other northern provinces.
In Haiphong, the strong winds smashed windows and waves were as much as three meters high when they hit the coast, according to a Reuters witness.
Metal roofing sheets were blown away, pictures and footage on local media showed. The government said thousands of trees had fallen and many houses were damaged across northern Vietnam.
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.
AIRPORTS CLOSED
Vietnam evacuated more than 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, which cancelled 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 meteorological agency has warned of risks of heavy flooding in the city centre.
Hanoi resident Nguyen Manh Quan, 40, said: "The wind is strong enough to blow a person over," while 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.
Last week, Typhoon Shanshan slammed into southwestern Japan, the strongest storm to hit the country in decades.
Yagi is named after the Japanese word for goat and the constellation of Capricornus.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)