On Tuesday, falling rocks killed one man in southeastern Taiwan, two women drowned in the north of the island, and a fourth victim was swept away by water while fishing in central Taiwan, the Centre for Disaster Response said.
A fisherman was also reported missing.
Dozens were injured, mostly by falling trees and signboards, as swollen rivers pounded bridges and knocked away roads.
At 5.10pm (0910 GMT), the typhoon hit the coastal Chinese town of Huangqi in Fujian province with winds of 119kph, said an official with the provincial weather bureau who identified herself only as Miss Li.
Heavy rain was falling over much of the southeastern province. State television showed villages awash with floodwaters that turned streets into rivers as well as soldiers delivering boxes of food to people living in temporary shelters.
More than one million people were evacuated from their homes in Fujian and Zhejiang province directly to the north, China Central Television reported.
One correspondent said the harsh winds felt like sand pelting his face.
But the winds weakened as the typhoon moved inland towards the northwest, and government forecasters predicted it would be downgraded to a tropical storm late on Tuesday, the official Xinhua News Agency said.
High winds are said to have
caused eight traffic accidents
The airport at Fujian's provincial capital, Fuzhou, was closed and flights were diverted north to Shanghai or south to Xiamen, the agency said.
Fuzhou is about 800km southwest of Shanghai, China's main commercial city.
Storm winds were blamed for eight traffic accidents on Monday on Fujian's main motorway, where billboards were blown away, Xinhua said. The report gave no figures on casualties.
China had been bracing for the storm for days, with soldiers stacking sandbags along embankments.
Even before the storm hit, the Sai river near the city of Fu'an in Fujian had surged to 1.85m above the official flood level, according to the website of the Fujian Water Management Bureau.
Haitang, named after a Chinese flower, hammered northern Taiwan on Monday.
Schools, government offices and financial markets were closed on Taiwan as torrential rains whipped through the capital, Taipei, uprooting trees and dislodging billboards in the island's north.
Taiwan's farms suffered damage estimated at $14.2 million, the Council of Agriculture said. No damage figures were immediately available for other industries.