At least 25 people, including 12 subway passengers, were killed when the heaviest rainfall in 1,000 years hit China’s central Henan province, official media reports said on Wednesday.
China's military has blasted a damaged dam to divert the surging waters of a flooded river.
A total of 1.24 million (12.4 lakh) people were affected and 1,60,000 evacuated, state-run Global Times reported.
The Army sent its troops early on Tuesday morning to a damaged dike in Yichuan county to explode it to divert the floodwater, state-run China Daily reported.
A total of 75 soldiers and soldiers of an engineering chemical defence brigade under the People's Liberation Army (PLA) Theatre Command completed the task of blasting and diverting the floodwater from the dam of Yihetan in Yichuan County at about 6 am and started follow-up rescue operations, China News Network reported.
The official media quoted local authorities as saying that 25 people were killed and seven others listed missing in the massive floods.
Twelve people were killed and five others injured when subway stations were hit by the floods, the report said. The victims died when their subway train was hit with rapidly rising floodwaters on Tuesday night, the Hong Kong-based South China Morning Post reported.
Two people were killed when a wall collapsed.
The massive floods, described by meteorologists as a once-in-a-lifetime event, has resulted in apocalyptic scenes in the provincial capital Zhengzhou, a metropolis of 12.6 million, with its public avenues and subway tunnels getting submerged with surging waters.
Videos posted on the Chinese social media showed petrified passengers trapped in subway trains clinging on to handlebars desperately waiting for help as floodwaters raised up to their necks.
Official media released videos of rescue workers helping people stuck in subway tunnels to safety.
Videos showed people trying to wade through floods in the downtown of the city while scores of cars and other vehicles washed away. Some videos also showed people falling into the massive cave-ins of the roads.
Rainwater poured into the subway tunnel of the city's Line Five, trapping an unknown number of passengers aboard a subway train.
Terming the flood situation as grim, Chinese President Xi Jiping ordered the deployment of the Army and said authorities at all levels must give top priority to ensuring people's safety and property as massive floods ravaged the province and Zhengzhou city.
The PLA Central Theatre Command urgently dispatched troops to a county in rain-hit Henan where a dam is under threat of collapse due to serious damage caused by the rains, state-run Xinhua news agency reported.
The PLA, on its social media account on Sina Weibo -- China's Twitter-like social media platform, said a 20-metre-long crevasse had appeared in the dam in Yichuan county of Henan province, and could collapse any time.
The downtown area of Zhengzhou received an average precipitation of 457.5 mm within 24 hours on Tuesday, the highest daily rainfall since the weather record began, Xinhua reported.
Henan is home to many cultural sites and a major base for industry and agriculture. Reports said Shaolin Temple, known for its Buddhist monks' mastery of martial arts, was also severely hit by the floods.
Heavy waterlogging has led to the virtual paralysis of the city's road traffic.
Over 80 bus lines have been suspended, more than 100 temporarily detoured and the subway service has also been temporarily suspended.
Police officers, firefighters and workers from the local sub-district have arrived at the site for the rescue operation, the report said.
The water level inside the subway carriage is receding, and the passengers are temporarily safe, it said.
More than 160 train services were stopped at Zhengzhoudong Railway Station. The airport in Zhengzhou cancelled 260 flights into and out of the city, and local railway authorities also halted or delayed some trains.
Affected by the rainstorms, several residential communities in the city are without tap water and electricity.
Both Henan provincial and Zhengzhou municipal meteorological bureaus have raised the emergency response for meteorological disasters to level I.
Heavy rains in Henan are expected to last until Wednesday night, according to forecasts.
Weather forecasters described the extreme event as the heaviest rainfall in 1,000 years, while hospitals have run out of electricity, the Post reported.
The Zhengzhou flood control headquarters issued a text message on Wednesday, warning residents there was a grave safety hazard in the Guojiazui reservoir and calling on them to evacuate the southwestern part of the city immediately.
Xinhua quoted President Xi as saying that the rainfall has made the flood control situation very severe, causing massive waterlogging in Zhengzhou and other cities, water levels in some rivers exceeding the alarm levels, and damages to dams of some reservoirs.
He said that sections of railways have also been shut down, and some flights have been cancelled.
Xi ordered authorities at all levels to promptly organise flood prevention and disaster relief forces, properly accommodate those affected, strictly prevent secondary disasters and minimise casualties and property losses.
He also stressed the need to take solid measures to assist those affected by the floods, and to strengthen hygiene and disease control so as to ward off epidemics and prevent people from returning to poverty due to disasters.