Water levels at China’s giant Three Gorges Dam on the Yangtze river are inching closer to their maximum after torrential rains raised inflows to a record high, official data showed on Friday.

With 75,000 cubic metres per second of water flowing in from the Yangtze river on Thursday, the reservoir’s depths reached 165.6 metres by Friday morning, up more than 2 metres overnight and almost 20 metres higher than the official warning level.

The maximum designed depth of China’s largest reservoir is 175 metres.

Authorities raised the discharge volume to a record 48,800 cubic metres per second on Thursday to try to lower water levels, and they might have to increase it again to avoid the possibility of a dangerous overflow.

“They will do everything they can to prevent the dam from overtopping,” said Desiree Tullos, a professor at Oregon State University who studies the Three Gorges project.

“An overtopping dam is a worst-case scenario because it produces significant damage... and can lead to the entire thing collapsing.”

Rainfall in the Yangtze basin has been well over double the seasonal average this year. The floods had caused nearly 180 billion yuan ($26 billion) in economic damages by last week, and 63 million people have been affected. The Three Gorges Project, completed in 2012, was designed to tame the fierce Yangtze.