BEIJING - Heavy rainfall in central China’s Henan province has killed 12 people in its capital, Zhengzhou, and has led to the relocation of about 100,000 people to safe zones, state media Xinhua reported on Wednesday (July 21) citing the local government.

Both Henan province and Zhengzhou municipal meteorological bureaus raised the emergency response for the disaster to level 1, with forecasts predicting heavy rains in the province to last until Wednesday night, Xinhua reported.

Henan province, which is double the size of Austria and has a population of 94 million people, has been hit by storms since the weekend in an unusually active rainy season, resulting in bursting of major river banks and flooding of streets of a dozen cities, upending daily lives of millions of people.

Overnight, local authorities announced that the rainfall had caused a 20m breach in the Yihetan dam in the city of Luoyang, and that the dam “could collapse at any time”.

A division of China’s People’s Liberation Army had been sent to the site for flood fighting and rescue, authorities added.

Separately, Zhengzhou’s flood control headquarters said that water storage at the Guojiazui reservoir is at “major risk” of dam failure and the local government was ordering evacuations.

The heavy rain has flooded the streets of a dozen cities and trapping subway passengers waist-high in floodwaters.

In Zhengzhou, more than 200mm of rain fell in one hour on Tuesday, forcing the city to stop all subway train services.

Dramatic video shared on social media showed commuters waist-deep in murky floodwaters on a subway train and an underground station turned into a large, churning pool.

Train services in Henan were suspended, while many highways were closed and flights delayed or cancelled.

Thousands of rescue workers including soldiers and firefighters have been dispatched to carry out rescue work.

The flooding came shortly after key Chinese cities warned that homes and factories face new power outages as historic demand and supply shortages strain energy grids. Eleven provinces including eastern manufacturing hubs and landlocked central China reported record demand and peak-load surges last week, amid hot weather.

In Ruzhou, a city south-west of Zhengzhou, streets have been turned into torrents, sweeping away cars and other vehicles, footage on social media showed.

A rising Yi River also threatened to hit the Longmen Grottoes, a Unesco World Heritage site featuring millennium-old Buddhist statues etched into limestone cliffs near the city of Luoyang.

Like the Longmen Grottoes, the Shaolin Temple in Dengfeng city, famous in the West for its martial arts, has been temporarily shut.

Also in Dengfeng, an aluminium alloy plant exploded on Tuesday as water from a river surged into the factory.

At least 31 large and medium-sized reservoirs in the province have exceeded their warning levels.

From Saturday to Tuesday, 3,535 weather stations in Henan saw rainfall exceed 50mm, of which 1,614 registered levels above 100mm and 151 above 250mm.

The highest was in Lushan city, which saw 498mm of rain, according to the provincial weather bureau.

"This is the heaviest rain since I was born, with so many familiar places flooded," said an Internet user in the inundated city of Gongyi on Chinese social media.

Rain is forecast to stop by Thursday.

Henan is a major producer of agricultural products and machinery, while Zhengzhou is home to a large plant owned by Taiwan’s Hon Hai Precision Industry, more commonly known as Foxconn.

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Floods are common during China’s rainy season, which causes annual chaos and washes 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.