The heavy rain hit parts of Dingxi City, Gannan Tibetan Autonomous Prefecture and the provincial capital Lanzhou last night, the provincial government said.
Seven people were killed and 26 others were injured. Nearly 20,000 people were affected and 213 houses collapsed, state-run Xinhua news agency reported today.
Flood and mud flow hit a township in Zhangxian County, Dingxi, damaging some houses and cut off a national highway.
Rescue and disaster relief work is under way. Authorities are also counting the exact losses of the disaster.