Days of heavy rain caused severe flooding in Central China. State news media said Wednesday at least 12 people trapped in a subway in Zhengzhou, the capital of China's Henan Province, had been killed.

The heavy rain caused rivers to overflow, sending water into urban areas in Henan province. State news media said floods breached a retaining wall near an entrance to Line 5 of Zhengzhou's subway system, flooding the underground tunnels.

Several passengers who were trapped in chest- and neck-deep waters were able to post videos online. In one video, water enters the windows of cars trapped inside the tunnel. Other videos showed corpses on a subway platform - suggesting that the death toll could be much higher.

The city of 5 million people is situated along the Yellow River. Zhengzhou's flood control headquarters said the heavy rains filled their water storage facilities, which are now at "major risk" of failure. The agency said they have already told local government officials to order an evacuation of affected areas. Xinhua News Agency said Wednesday at least 100,000 people have been moved to temporary shelters

Authorities said they have already dispatched military personnel to help in the rescue operations. Heavy rains in China's Henan province started Tuesday and have not yet ceased. China's weather agency said more than 20 centimeters of rain fell in just one hour at the start of the downpour.

Local authorities in the city of Luoyang warned that the Yihetan dam could "collapse at any time." Weather authorities have issued the highest warning level for the province as further downpour is expected throughout the rest of the week.

Cities near Zhengzhou also reported severe flooding. Residents from nearby cities posted pleas for help on social media. According to local reports, about 20,000 people had to be evacuated in Gongyi after floodwaters inundated hundreds of homes.

Floods are common in urban areas situated along China's rivers and streams. However, the severity of floods in recent years has dramatically increased despite the government's flood control efforts. Last summer, hundreds of people were killed and millions displaced after several areas along the Yangtze River were flooded following heavy rain.