Heavy rains killed 21 construction workers as flooding spread to northwest China, state media said Wednesday, after severe weather in other parts of the country left more than 130 dead.

Sudden rainstorms and hail battered Haixi in Qinghai province, "washing away" the workers on Tuesday evening, the official Xinhua news agency said.

"The workers were repairing a construction site at the time when the tragedy happened," it added.

A search for three missing people was under way.

Meanwhile, Chinese Premier Li Keqiang called for "persistent efforts" to save victims from what Xinhua described as "the worst floods in decades" in northeast China.

Authorities said 85 people in the region were confirmed dead, 105 missing, and some 3.74 million people had been affected by the severe weather.

The worst-affected province was Liaoning, where Xinhua quoted Guo Shouying, 54, as saying: "Floodwater gushed out of the embankments and my mother was swept away.

"The neighbours heard her desperate calls for help, but the flood was so huge that no one dared to swim into the water to rescue her."

Her mother's body was found 100 metres from her home in Xinbin the next day.

"One hand pressed her nose and her mouth was wide open, she was probably choked by water," said Guo tearfully.

Another 49 people have perished in Hunan, central China, and in the southern provinces of Guangdong and Guangxi, the ministry of civil affairs announced.

Nearly 3,000 military personnel were mobilised to help with the relief efforts, Xinhua reported earlier.