At least 21 people have been killed and four reported missing in floods and mudslides that hit a Chinese province where at least 95 others died this week in twin earthquakes, state media reported on Saturday.

Floods, landslides and rockfalls have been reported since Thursday in the northwestern province of Gansu following heavy rains, China's official Xinhua news agency said, quoting the local government.

Several villages in the province were cut off, with power and communication lines down and roads blocked, the government said.

In one village, named Rongguang, more than half of the houses had been destroyed in the disasters, said a rescuer.

Xinhua said 30,000 people had been evacuated, with more heavy rain forecast.

Gansu was hit by twin earthquakes with magnitudes of 5.9 and 5.6 on Monday.