In Wuhan, Hubei Province, eight dead and 280 injured were reported.
About 30 houses have been completely destroyed and over 130 damaged.
In Jiangsu, which is often hit by tornadoes during the spring and summer, four people have been reported dead and about 150 injured.
According to the rescue service, the strong winds have also destroyed parts of the electricity grid as well as several houses and factories.
Also in Shanghai, the authorities have issued warnings due to continued heavy thunderstorms on Saturday.