But even senior dam officials who have often defended the project as an engineering wonder and ecological boon now warn that areas around the dam are paying a heavy, potentially calamitous environmental cost.

"There exist many ecological and environmental problems concerning the Three Gorges Dam," the senior officials were quoted as saying. "If no preventive measures are taken, the project could lead to catastrophe."

The US$25 billion dam, whose construction flooded 116 towns and hundreds of cultural sites, is still a work in progress, but state media have said it could be completed by the end of 2008, just after the Beijing Olympic Games.

Wang Xiaofeng, director of the administrative office in charge of building the dam, told the forum that it was time to face up to the environmental consequences of constructing the massive concrete wall across the country's biggest river.

"We absolutely cannot relax our guard against ecological and environmental security problems sparked by the Three Gorges Project," Wang told the meeting, according to Xinhua.

"We cannot win passing economic prosperity at the cost of the environment."

LITANY OF THREATS

Wang cited a litany of threats, especially erosion and landslides on steep hills around the dam, conflicts over land shortages and "ecological deterioration caused by irrational development".

The strikingly frank acknowledgement of problems comes weeks before a congress of the ruling Communist Party that is set to consolidate policies giving more attention to environmental worries after decades of unfettered industrial growth.

Wang revealed that Premier Wen Jiabao had used a cabinet meeting earlier this year to discuss the environmental problems surrounding the dam.

Tensions over residents resettled to steep hills where good farmland is scarce had been reduced and water quality in the dam was "generally stable", Xinhua said.

But the officials and experts were worried about the landslides threatening densely populated hill country.

"Regular geological disasters are a severe threat to the lives of residents around the dam," senior engineer Huang Xuebin told the forum.

Huang described landslides into the dam waters making waves dozens of metres high that crashed into surrounding shores, creating even more damage.