Record rains kill 25 in central China

At least 25 people have died after torrential rains caused landslides and flooded a city in central China, with shocking images showing passengers struggling against chest-high water inside a train carriage.

As 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.

Around 200,000 residents were evacuated in Zhengzhou, local government officials said, as soldiers led rescue efforts in the city of over 10 million people which saw the equivalent of a year's average rain dumped on it in just three days.

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The rainfall in the region was the heaviest since record-keeping began 60 years ago.

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

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.

At least four were killed in nearby Gongyi city where houses and walls have collapsed, the official Xinhua news agency said, adding that rainfall had caused multiple landslides.

Relatives outside Zhengzhou 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."

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Authorities have issued the highest warning level for Henan province as floods continue to hammer the region, with landslides blocking many roads, villages evacuated and large areas left without communication.

As the scale of the disaster continued to unspool and the damage ran into tens of millions of dollars, the Chinese army said it had averted the collapse of the stricken Yihetan dam around an hour from Zhengzhou city.

On Wednesday morning, the People's Liberation Army said blasting operations had been carried out at the dam and troops had "successfully opened a new flood diversion opening".

These measures meant the water level had dropped and the "danger has been effectively controlled".

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

"Some reservoirs had their dams burst... causing serious injury, loss of life and property damage," 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.