Forty people have been killed after a brief but violent hailstorm and torrential rain swept through a mountainous region of northwest China, the local government has said.

Eighteen others remain missing in Min county in Gansu province, while 87 have been sent to hospital, the county government said in a statement on its website on Sunday.

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

It has "wreaked havoc" on all of the county's 18 townships and 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.

Rainstorms have battered some regions in east, central and southwest China since Saturday, causing sharp rises in river water levels and damage to roads and properties.

Strong downpours hit the cities of Yichun and Nanchang in east China's Jiangxi Province on Saturday.

In Zhangjia village of Yifeng County in Yichun, heavy rainfall resulted in floods. Local government dispatched rescuers to evacuate residents who were trapped by the rising waters.

Rainstorms have also struck parts of central China's Hunan province since Saturday morning.

It is forecast that rainfall will continue at least until Monday, and meteorologists have warned of possible geological disasters such as landslides.