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 depth had reached 165.6 metres (543 feet) by Friday morning, up more than two metres (6.6 feet) overnight and almost 20 metres (65.6 feet) higher than the official warning level.

The maximum designed depth of China's largest reservoir is 175 metres (574 feet). 

Authorities raised the discharge volume to a record 48,800 cubic metres per second on Thursday to try and 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, the world's biggest hydroelectric dam.

"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. Up to last week, 63 million people had been affected by flooding, which had caused nearly 180 billion yuan ($26bn) in economic damage.

The Three Gorges, completed in 2012, was designed not only to generate power but also to reduce the risk of flooding from the Yangtze, the cause of many devastating floods throughout China's history.

Yangtze River's fifth flood peak this year reached the Three Gorges Dam, with a reservoir inflow of 75,000 cubic meters per second, according to the #YangtzeRiver hydrological Network. #ChinaFloods2020 #Hubei #ThreeGorgesDam #三峡大坝 pic.twitter.com/bQB747Zqh7

— CGTN Culture (@CGTN_Culture) August 21, 2020

China's giant hydroelectric dams have stored more than 100 billion cubic metres of floodwater this year, and shielded 18.5 million residents from evacuation, according to government figures. The Three Gorges project alone has cut downstream floodwaters by 34 percent, officials said.

But opponents say the flood control capability of the Three Gorges Dam is limited, and it could even make the problem worse in the long term.