SHANGHAI (REUTERS) - China's controversial Three Gorges Dam, the world's biggest hydropower project, is structurally sound, officials said, denying rumours on social media that it was at risk of collapse.

Safety experts with the government-run China Three Gorges Corporation said on its official website that the Yangtze River dam had moved a few millimetres due to temperature and water level changes, but safety indicators remained well within their normal range.

They were responding to a Twitter user who posted satellite photos from Google Maps last week purporting to show the dam had bent and was at risk of breaking. The photos were circulated on domestic social media.

The central government said the problem was with the satellite imaging, rather than the dam, the Caixin financial news service reported on Tuesday (July 9), citing a statement.

The 185m-high Three Gorges Dam is one of China's most expensive and most controversial engineering projects, submerging entire villages, displacing millions of people and disrupting ecosystems.

Critics say it has also increased earthquake and landslide risks in the region.

In 2011, five years after the dam was built, China admitted the project had caused widespread social and environmental damage and promised 124 billion yuan (S$24.5 billion) in extra funding.

A parliamentary delegate said this year that half of the promised money had still not been paid out.

Mr Fan Xiao, a Chinese geologist and longstanding critic of giant dam projects, said the rumours reflected the lack of debate about the Three Gorges project, which is now considered a "national treasure" that should not be criticised.

"If talking about problems is stigmatised, then it is nothing more than putting one's head in the sand and deceiving oneself," Mr Fan posted on his WeChat account on Monday. "It will solve no problems and could make them worse."