Shanghai relocated more than 280,000 people, halted hundreds of flights and ferry services and imposed speed limits on roads and railways on Wednesday as a tropical storm whipped eastern China with gales and heavy rain.

Co-May's landfall in the port city of Zhoushan in Zhejiang province in the early hours of Wednesday was soon followed by warnings of a tsunami set off by a powerful earthquake off Russia's far east, raising concerns of larger-than-expected storm surges along the Chinese coast.

While the winds from Co-May were weaker than those generated by typhoons, the financial hub and other cities in the Yangtze River delta have taken no chances.

At least 640 flights could be cancelled at Shanghai's two main airports on Wednesday, including 410 at Pudong and 230 at Hongqiao, authorities said.

All ferry services in Shanghai had been cancelled since Wednesday morning, and drivers were told to drive under 60 kilometres per hour on highways, local media reported.

Airports at nearby cities Ningbo, Wenzhou and Hangzhou also saw flight cancellations and diversions.

As of Wednesday morning, more than 75 percent of the day's flights at Zhoushan had been cancelled.

Some train services in the region were temporarily suspended with others operated under restricted speeds, state media.

Co-May made landfall in Zhoushan in the early hours of Wednesday with maximum sustained wind speeds near its centre of 83 kilometres per hour. Forecasters expect Co-May to make another landfall closer to Shanghai later on Wednesday. (Reuters)