The lightning, rain and violent winds that hit Hainan also injured 92 people, Chinese state media said on Saturday, citing local authorities.
Yagi made landfall in Hainan on Friday, packing maximum sustained winds of 234km/h near its centre, downing trees and flooding roads.
Super typhoon Yagi is churning towards northern Vietnam after tearing through southern China. (AP PHOTO)
Power supply to more than 800,000 homes was cut.
The island province of more than 10 million people remained in a state of paralysis, with emergency workers only starting to clear debris, uprooted trees and overturned vehicles.
Yagi formed over the sea to the east of the Philippine archipelago on September 1.
Gaining strength, it became a tropical storm and swept across Luzon, the most populous island in the Philippines, killing at least 16 people and injuring 13.
The storm grew dramatically stronger late in the week, becoming the world's most powerful tropical cyclone in 2024 after the category five Atlantic hurricane Beryl, and the most severe in the Pacific basin so far in 2024.
Yagi was spinning towards northern Vietnam over the Gulf of Tonkin on Saturday.
Maximum wind speeds that had slightly eased earlier on Saturday picked up pace again, reaching category four velocities of 216km/h, according to Chinese meteorological authorities.
