Saomai was expected to hit the mainland on Thursday in Fujian and Zhejiang provinces, where heavy rains were expected, the Xinhua News Agency said, citing government forecasters.
Saomai, named for the Vietnamese word for the planet Venus, would be the eighth powerful storm to hit China during this year's unusually violent typhoon season.
At midday on Thursday, the storm was moving northwest across the East China Sea toward the coast at 20 mph (30 kph), with winds of up to 135 mph (216 kph), Xinhua said.
In Fujian, more than 36,000 vessels had returned to harbors and outdoor activities at 26,800 schools were suspended, the agency reported, according to the AP.
The storm was headed toward areas that were pounded last month by Tropical Storm Bilis, which killed more than 600 people.
Another typhoon, Prapiroon, lashed China's southern coast last week, killing at least 80 people.
More than 167,000 people have been evacuated from vulnerable coastal areas of Zhejiang, while 266,000 have been evacuated in Fujian, Xinhua said.
In Hong Kong, the Airport Authority said that six flights departing to Taiwan were canceled on Thursday morning, while 11 others were delayed.
On Wednesday, Saomai passed across the Japanese island group of Okinawa with winds up to 144 kph, prompting airlines to cancel 141 flights and affecting 24,000 passengers.
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