At least one person was killed, China National Radio (CNR) said in an online report.
Parts of Zhejiang province near the commercial hub Shanghai saw nearly 29 centimetres (11 inches) of rain over 17 hours from Sunday to early Monday, while areas in Fujian to the south saw up to 16 centimetres, the official China News Service said.
One person was reported dead in Wenzhou, a major city in Zhejiang where more than 1,200 homes collapsed CNR said, although it was not clear whether the person died in one of those houses.
Authorities evacuated hundreds of thousands of people and issued China's highest alert on Sunday as Typhoon Fitow approached the mainland.
The National Meteorological Centre issued a red alert for the storm, which was packing winds of up to 151 kilometres (94 miles) an hour late Sunday night as it moved towards the coast.
Winds rose to 201 km per hour in parts of Wenzhou, the official Xinhua news agency reported later, citing local flood control authorities.
Zhejiang has so far evacuated more than 574,000 people, while in Fujian 177,000 have been displaced, Xinhua said.
Two port workers in Wenzhou were missing and may have fallen into the sea, the agency added.
"We must not leave anybody in danger," said Li Qiang, Zhejiang's provincial governor.
He urged local authorities to increase inspections of dams and reservoirs as well as safety checks of chemical plants and other important facilities, Xinhua reported.