The death toll in central China's unprecedented flash floods triggered after the heaviest rainfall in 1,000 years has reached 33 with eight people missing, while officials raced to evacuate patients and medics stuck in waterlogged hospitals in the flood-hit Zhangzhou city.

The torrential rain has affected about three million people in Henan province and a total of 376,000 local residents have been relocated to safe places, the provincial emergency management department said.

A day after the worst floods, officials raced to evacuate patients as hospitals were flooded by rainstorms, state-run Xinhua news agency reported on Thursday.

The natural disaster has inflicted damage to many hospitals in Henan, with patients and medical staff stuck inside, waiting to be evacuated, including in the Fuwai Central China Cardiovascular Hospital in the county of Zhongmu that falls under the jurisdiction of Zhengzhou, the provincial capital.

Days of rainstorms have caused severe flooding in the Fuwai hospital. On Thursday morning, rescuers started transporting patients, their family members and medical staff elsewhere. About 5,000 people have been evacuated so far.

”We have 1,075 regular patients and 69 in severe conditions, and the number of family members is about 1,300,” Gao Chuanyu, vice president of the hospital told Xinhua.

”Most people will be brought to safety by rafts, but for critically ill patients, we need to use helicopters,” Gao said. Another hospital that has been damaged is the Heyi branch of the First Affiliated Hospital of Zhengzhou University in Zhengzhou. Built on low-lying land, the area was heavily flooded.

Starting on Tuesday evening, a blackout struck the hospital, endangering the lives of about 600 patients suffering from severe medical conditions, the report said.

On Wednesday morning, the water had swallowed many cars near the entrance, and medical staff were using rafts to transport supplies to the patients.

Fortunately, rescuers from across the country managed to evacuate people to safety, it said.

Rainwater has damaged more than 215,200 hectares of crops, causing a direct economic loss of about 1.22 billion yuan (about USD 188.6 million), state-run Xinhua news agency reported.

The massive floods, described by meteorologists as a once-in-a-lifetime event, has resulted in apocalyptic scenes in Henan and its capital Zhengzhou, a metropolis of 12.6 million, with its public avenues and subway tunnels getting submerged with surging waters.

China's People's Liberation Army (PLA) blasted a damaged dam to divert the surging waters of a flooded river after the province received the heaviest rainfall in 1,000 years.

Twelve people were killed and five others injured when subway stations were hit by the floods. The victims died when their subway train was hit with rapidly rising floodwaters on Tuesday night. Two people were killed when a wall collapsed.

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, President Xi Jinping ordered the deployment of the PLA 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.

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.

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.

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.