Severe rainstorms kill 12 in flooded China subway

Twelve people died after torrential rains flooded a subway in the central Chinese city of Zhengzhou, as shocking images showed passengers struggling against chest-high water inside a train carriage.

As dams burst and river embankments were breached in record downpours across Henan province, President Xi Jinping described the situation as "extremely severe" with flood control measures entering a "critical stage", state media reported Wednesday morning.

Around 200,000 city residents were evacuated, local government officials said, with soldiers leading rescue efforts in the city of over 10 million people, where days of rain have inundated the streets and subway.

Rainstorms submerged Zhengzhou's metro, killing 12 people and injuring five, while hundreds were rescued from the subway, city officials said in a Weibo post.

Nerve-shredding images shared on social media showed shocked passengers contending with the fast-rising waters inside a train carriage. Rescuers cut open the roof of the coach to pull people to safety, local media reported.

Others showed dramatic rescues of pedestrians in Zhengzhou from torrents gushing through the streets.

Relatives outside the city made anxious pleas on China's Weibo for information as communications to the city went down.

"Is the second floor in danger? My parents live there, but I can't get through to them on the phone," one user wrote.

"I don't know more about their situation. I'm in Tianjin and my parents are in Zhengzhou," she said, giving her surname only as Hou when contacted by AFP.

"I'm very anxious."

Authorities have issued the highest warning level for Henan province as floods continue to hammer the region.

As the scale of the disaster continued to unspool on Wednesday, the Chinese army warned that a stricken dam around an hour from Zhengzhou city "could collapse at any time" after being severely damaged in torrential storms.

The regional unit of the People's Liberation Army alerted Tuesday that the relentless downpour had caused a 20-metre breach in the Yihetan dam in Luoyang — a city of around seven million people.

The PLA's Central Theater Command said it had sent soldiers to carry out an emergency response including blasting and flood diversion.

"On July 20, a 20-metre breach occurred at the Yihetan dam.... the riverbank was severely damaged" it added in the statement.

Soldiers have been deployed to other rivers nearby to reinforce embankments with sandbags as the floods fanned out across Henan and warnings were issued of other near breaches of dams.

"Some reservoirs had their dams burst... causing serious injury, loss of life and property damage," Chinese President Xi Jinping said, according to state broadcaster CCTV.

"We have already entered the critical stage of flood control, leaders and cadres from all walks of life must... take the lead in commanding, quickly organise forces for flood protection and disaster rescue."

Annual floods during China's rainy season cause chaos and wash away roads, crops and houses.

But the threat has worsened over the decades, due in part to widespread construction of dams and levees that have cut connections between the river and adjacent lakes and disrupted floodplains that had helped absorb the summer surge.

Scientists say climate change is also worsening flooding around the world alongside other increasingly extreme weather patterns.

According to the authorities, the rainfall in the region was the heaviest since record-keeping began 60 years ago, with Zhengzhou seeing the equivalent of a year's average rainfall in just three days.