Typhoon Morakot battered China's commercial east coast on Sunday, killing a child and flattening houses.
Half a million people in coastal Fujian province were moved to safer parts ahead of the typhoon's arrival, along with a similar number in neighboring Zhejiang, Xinhua reported.
Up the coast, Shanghai was on "high alert" and dozens of cargo ships in the area delayed or canceled voyages. China's National Meteorological Center said "violent rainstorms" could strike swathes of eastern China on Sunday and into Monday.
Winds of up to 120 kph (75 mph) destroyed five houses in Wenzhou, a manufacturing hub on the coast of Zhejiang, the official news agency said.
"Four adults and a four-year-old boy were buried in debris and the child died during the afternoon after emergency treatment failed," Xinhua said, citing city officials.
The typhoon had swept across Taiwan, the self-ruled island off the Chinese coast, killing three people, and 27 were missing, Taiwanese disaster response officials said on Sunday.
A hotel in Taiwan collapsed into a swollen river after guests and staff had been evacuated.
The winds were set to weaken as the typhoon crossed the Chinese mainland but business, fishing and shipping across the export-driven eastern region was likely to be badly disrupted.
Many flights across the region were canceled. At least one cargo ship was beached by the winds and waves.
Typhoons regularly hit China, Taiwan, the Philippines and Japan in the second half of the year, gathering strength from the warm waters of the Pacific Ocean or South China Sea before weakening over land.