Forty people were killed when a brief but violent hailstorm and torrential rain swept through a mountainous region of northwest China, according to the local government.

Eighteen others remained missing in Min county, a disaster-prone area of Gansu province, while 87 had been sent to hospital, the county government said in a statement on its website.

Officials said 29,300 people had been evacuated after rain and hail battered the county for just 60 minutes late Thursday afternoon.

It had "wreaked havoc" on all of the county's 18 townships and had affected more than two-thirds of its 450,000 residents, the state-controlled Xinhua news agency reported.

"Roads were blocked, houses collapsed, farmland was destroyed, and the power supply and telecommunications services were disrupted by the extreme weather," the agency said, quoting Xu Guangyao, a senior county official.

Min county is 150 kilometres (94 miles) from Zhouqu county, where a rain-triggered mudslide killed about 1,500 people in August 2010.