The monster storm made landfall in the early hours in Wenling City packing winds of 187 kilometres per hour (116 miles per hour), and was expected to churn up the east coast towards Shanghai, Xinhua news agency said.
More heavy rain was forecast for the Shanghai area as well as the eastern provinces of Anhui, Fujian, Jiangsu and Zhejiang, with authorities warning of possible flash floods, mudslides and landslides caused by the downpours.
In Zhejiang province alone, nearly 300 flights were cancelled, and ferry and rail services were suspended as a precaution.
More than a quarter of a million people were relocated in Shanghai, where the high-speed maglev train that links the city to one of its airports was suspended.
More than 110,000 people were housed in shelters.
China issued a red alert as the storm approached on Friday, before downgrading the level to orange as winds eased on Saturday morning.
The storm had earlier swept past the northern tip of Taiwan on Friday, where nine people were injured, thousands of homes lost power temporarily and more than 500 flights were cancelled.
Last September, Typhoon Mangkhut slammed into mainland China where authorities evacuated more than two million people, after it left a trail of destruction in Hong Kong and Macau and killed at least 59 people in the northern Philippines.
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