Winds have been recorded at up to 187km/h (116 mph) and about 400 flights have been cancelled.
The storm left five people dead in the Philippines earlier in the week. It also hit Taiwan and Japan, uprooting trees and injuring several people.
China`s National Meteorological Centre warned that Chan-hom could be the worst typhoon to strike the region since 1949.
It was forecast to make landfall in Zhejiang province near the port city of Ningbo, before moving towards Shanghai.
The BBC`s John Sudworth in Shanghai says the city is already feeling the power of the storm, with high winds and heavy rain.
Officials in Zhejiang have called nearly 29,000 fishing boats back to port amid reports of waves up to 10m (33ft) high, the official Xinhua news agency reported.
Chinese television showed footage of coastal regions being battered by torrential rain as the typhoon neared.
More about:
