* Henan province hit by heavy rains since weekend
* Provincial capital Zhengzhou, dozen other cities flooded
* 12 die in flooded Zhengzhou subway line, more than 500 rescued
* Numerous rivers swollen, some reservoirs breached
* Foxconn says 'no direct impact' on Zhengzhou iPhone assembly plant
BEIJING, JULY 21
Large swathes of China's central Henan province were under water on Wednesday, with its capital Zhengzhou hardest-hit after being drenched by what weather watchers said was the heaviest rain in 1,000 years.
In Zhengzhou, a city of over 12 million on the banks of the Yellow River, 12 people died in a flooded subway line while more than 500 were pulled to safety, the local government said.
Video on social media on Tuesday showed commuters chest-deep in murky floodwaters on a train in the dark and an underground station turned into a large, churning pool.
"The water reached my chest," a survivor wrote on social media. "I was really scared, but the most terrifying thing was not the water, but the increasingly diminishing air supply in the carriage."
Due to the rain, the authorities halted bus services, as the vehicles are powered by electricity, said a Zhengzhou resident surnamed Guo, who spent the night at his office.
"That's why many people took the subway, and the tragedy happened," Guo told Reuters.
From the evening of Saturday until late Tuesday, 617.1 millimetres (mm) of rain had drenched Zhengzhou - almost on par with the city's annual average of 640.8 mm.
The amount of rainfall in Zhengzhou witnessed over the three days was one seen only "once in a thousand years", local media cited meteorologists as saying.
The lives of millions of people in Henan have been upended in an unusually active rainy season that has led to the rapid rise of a number of rivers in the vast Yellow River basin.
Many train services across Henan, a major logistics hub in central China, have been suspended. Many highways have also been closed and flights delayed or cancelled.
Taiwanese technology giant Foxconn operates a plant on the outskirts of Zhengzhou, next to the city's airport, that assembles iPhones for Apple. Foxconn said it had activated an emergency response plan for flood control.
"We can confirm that there has been no direct impact on our facility in that location to date," it said in a statement.
Roads in a dozen cities have been flooded. Videos on social media showed residents wading across streets in fast-moving water. One video showed an adult and a child being swept away on a major artery choked with half-submerged vehicles.
Dozens of reservoirs and dams also breached warning levels.
Local authorities said the rainfall had caused a 20-metre breach in the Yihetan dam in Luoyang city west of Zhengzhou, and that the dam "could collapse at any time".
In Zhengzhou, the local flood control headquarters said the city's Guojiazui reservoir had been breached.
About 100,000 people in Zhengzhou have been evacuated to safe zones.
"Flood prevention efforts have become very difficult," President Xi Jinping said on Wednesday, addressing the situation in a statement broadcast by state television.
Zhengzhou's transportation system remained paralysed, with schools and hospitals cut off by waterlogging. Some children have been trapped in their kindergartens since Tuesday.
The First Affiliated Hospital of Zhengzhou - a large treatment centre with over 7,000 beds - has lost all power, and even backup supplies were down, the People's Daily reported.
The hospital was racing to find transport to relocate about 600 critically ill patients.
Heavy rain is forecast to persist through Wednesday, though precipitation will continue across the province for the next three days.