The subway train in Zhengzhou, a city of five million in central China, was approaching its next station when the floodwaters began to rise ominously on the tracks. The passengers crowded forward as the water rose, submerging the cars at the rear first because they were deeper in the tunnel.
As the water reached their waists, then chests, finally their necks, the passengers called emergency services or relatives. One gave her parents the details for accessing her bank account. Some cried. Others retched or fainted. After two hours, it became difficult to breathe in the congested air that remained in the cars.
Ding Xiaopei, a radio host, was afraid to call her children, 13 and 4. What could she say? She posted a video that she thought might be her last message. “The water outside has reached this position,” she said, it having reached chest level, “and my mobile phone will soon run out of power.”
“Please save us!” she wrote.
The flood that inundated Line 5 of Zhengzhou’s subway on Tuesday added to the grim global toll extreme weather has taken already this year, with scorching heat in the Pacific Northwest, forest fires in Siberia, and flooding in Germany and Belgium. Although flooding is common in China, researchers have attributed the extreme weather sweeping the planet to the consequences of climate change.
At least 25 died in and around Zhengzhou, the capital of Henan Province, including 12 people in the subway, according to officials who briefed journalists on Wednesday. Days of torrential rain that began on Sunday created scenes of destruction that suggested the death toll could rise much higher.
Aerial photographs showed scores of cars in Zhengzhou all but submerged, the fate of their drivers and passengers unknown. Videos circulating online showed cars and even people being swept away in churning torrents.
The First Affiliated Hospital of Zhengzhou University, one of the country’s largest, filled with floodwater, losing electricity and jeopardizing patients being treated or monitored with electrical medical devices. The subway remained closed through Wednesday evening.
With the rain still falling, nearly 10,000 people were trapped aboard passenger trains in Henan, unable to move because water covered the tracks, the newsmagazine Caixin reported. At least one carrying 735 people came to a stop near Zhengzhou and, after more than 40 hours, had run out of food and water. By the afternoon, some passengers were able to leave, while railway workers brought supplies to those still waiting aboard for service to resume.
In a sign of the severity of the disaster, China’s leader, Xi Jinping, ordered the authorities to give top priority to people’s safety, Xinhua, the state-run news agency, said in a report that described “heavy casualties and property losses” without providing specific figures. Mr. Xi called the flooding “very severe” and warned that some dams had been damaged even as rivers exceeded alert levels.
Mr. Xi’s directive mobilized soldiers from the Central Theater Command of the People’s Liberation Army to help with rescue efforts and to shore up the Yihetan Dam near the city of Luoyang, about 75 miles upstream from Zhengzhou, after it suffered a 65-foot breach.
The rain in the area was the heaviest on record in the city, according to China’s state television network, CCTV. At one point, the city saw nearly eight inches of rain in one hour. In one day, the region recorded roughly the average annual rainfall.
Flooding was reported in several cities and towns, where people posted pleas for help on WeChat and Weibo, two of the country’s biggest social networks. In the city of Gongyi, at least 20,000 people were displaced by floodwaters that inundated scores of homes, while mudslides washed away roads and cut off some villages. At least four people were killed in that area.
Across the province, more than one million people have been affected by the floods, the officials said, though they said only seven people were reported missing by Wednesday evening.
China has a history of catastrophic floods and the ruling Communist Party has tried to tame the country’s volatile rivers and streams, but the risks of extreme weather appear to have increased, overwhelming drainage systems and rescue efforts and posing a test to the leadership.
Last summer, China battled weeks of flooding along the Yangtze River that killed hundreds of people and displaced millions more. The rains at that time filled the Three Gorges Dam to its highest level since it opened in 2003, raising fears that the dam itself could fail.
The government often goes to great lengths to manage information about disasters, sensitive about its history of underreporting casualties. It is quick to limit news coverage and censor blogs and social media sites to mute public dissatisfaction with prevention and rescue efforts.
Some people on Chinese chat platforms and social media sites have raised questions about whether official news outlets in Zhengzhou and Henan Province initially downplayed the flood. When storms struck Beijing recently, the authorities warned people to stay home, but there was no order to shut businesses or schools in Zhengzhou ahead of Tuesday’s heavy rain.
In times of disaster, the country’s state news media often focuses on the efforts of rescue workers, including the military, while playing down the causes of disasters and their damage. A journalism professor, Zhan Jiang, posted a note on Weibo, the social media platform, on Tuesday complaining that a television station in Henan Province continued to show its regular programming instead of providing public safety information.
The terror in Zhengzhou’s subway began on Tuesday evening when floodwaters breached a retaining wall near an entrance to Line 5, which makes a loop around the city center. The water poured into the system between the Shakou Road and Haitan Temple stations, trapping the train Ms. Ding was riding with her husband at 6:10 p.m.
Trapped passengers posted videos that quickly circulated online as the disaster unfolded. In one, water surged outside the subway car’s windows. Other photographs and videos — some later apparently removed by censors — showed several lifeless bodies on a subway platform at the Shakou Road station.
“It’s like making a horror movie, my goodness,” one man trapped in a subway car could be heard saying in one video.
With the air running out, someone used a fire extinguisher to break through a window in the roof, allowing in fresh air, Ms. Ding said in her posts and in an interview with the news site Jiemian, part of the state-owned Shanghai United Media Group.
By 8:35 p.m., rescuers reached the train and devised a pulley system with ropes to help passengers pull themselves through the floodwaters along a ledge in the subway tunnel. The elderly and injured went first, followed by the women and then the men. State news organizations said that 500 people were evacuated in all.
One man still missing was Sha Tao. When the subway car first flooded, he called his wife and asked her to call the police. She has not heard from him since. She posted a message on Weibo asking people for help, describing his height and weight and the clothes he was wearing.
“I haven’t found him yet,” she said when reached by telephone in Zhengzhou on Wednesday. “I went to several hospitals, but the hospitals didn’t have any information and couldn’t find him. His phone is now off.”
Amy Chang Chien, Claire Fu, Li You, Liu Yi and Albee Zhang contributed research.