At least 12 people have been confirmed dead in Zhengzhou, the provincial capital, where more than 20 centimeters (7.8in) of rain fell in one hour on Tuesday, according to the meteorological observatory.
More than 100,000 people have so far been evacuated from Zhengzhou, a city of 12.6 million on the banks of the Yellow River, with thousands of emergency personnel deployed to assist in the effort, according to state-run media.
All of the bodies recovered were taken from the city's subway system, according to provincial authorities.
In the nearby city of Gongyi, at least four were confirmed dead and more than 20,000 people have been forced to leave their homes, state media reported Wednesday.
Chinese President Xi Jinping addressed the flooding on Wednesday morning, calling the flood control situation "very severe" and ordering authorities to "prioritize the safety of people's lives and properties," state news agency Xinhua reported.
A manicured hand touches the train carriage window as a brown swirl of floodwater squeezes up against the tunnel outside one of many scenes of desperation from an underground tragedy shared Wednesday across a stunned Chinese social media.
Social media platform Weibo and local media outlets carried fragments of the horror video posts seemingly made as a final testimony of chest-high and rising water inside carriages as lights went out on the city's 'Line Five' during the commuter rush hour.
'I can't speak anymore, please help'
Footage broadcast by Xinhua and shared widely online shows passengers in Zhengzhou trapped inside a flooded subway car, packed tightly together as the water climbs higher. Outside the window, dark floodwater rips past, surging down the subway tracks.
Many of those trapped posted calls for help on social media, according to screenshots circulated online and statements from the Henan fire department.
"The water inside the carriage has reached chest-levels! I already can't speak anymore, please help!" wrote one woman, who went by the name Xiaopei.
Minutes later, she posted another comment: "If no rescue comes in 20 minutes, several hundreds of us will lose our lives in Zhengzhou subway." The fire department later confirmed Xiaopei had been rescued.
The city's subway system, which contains seven lines and 153 stations, suspended all operations after the incident, said provincial authorities.
Other videos show residents on the street, water up to their hips, working desperately to pull out people trapped in an underground mall using ropes. One clip shared by state-run newspaper People's Daily shows motorists on a road making a human chain, to prevent being swept away by the current as they struggle through rushing water.