The Xinhua news agency said 19 of the 22 gates at the dam in Yichang, in the central province of Hubei, closed by 9.20 a.m. (0120 GMT), blocking the flood-prone Yangtze to form what will become a 600-km (365-mile) reservoir.

"The project to close the gates to fill the Three Gorges reservoir is successful," it said.

China says the world's largest hydroelectric project is critical for national power needs and will help tame the 6,300 km (3,900 mile) Yangtze, whose annual floods killed 300,000 people in the last century alone.

"When the entire project is completed in 2009, it will be highly effective for flood control, power generation, navigation, ecological protection and water diversion," Xinhua said.

But critics at home and abroad say the $25 billion project, begun in 1993, will bring ecological disaster as pollution seeps from the remnants of deserted towns, villages, factories and hospitals on the reservoir bed.

More than 720,000 people - from fishermen to farmers - along the Yangtze were uprooted, and more than one million million will move before the reservoir swallows lands - and some archaeological treasures - across about a dozen counties.

The project also has been plagued over the past decade by corruption and discovery of hundreds of cracks in the dam, though the Guangzhou Daily on the weekend quoted officials as saying the cracks, some tens of metres (yards) long, were not a danger.

UPROOTED

Despite the live coverage, word of the event failed to reach the ears of many relocated to Chongming Island at the mouth of the Yangtze far to the east near Shanghai. Farmer Ke Chungui, 49, heard of it first from a foreign reporter and then caught the broadcasts on a radio.

Ke, his feet clad in straw shoes, said he had been unable to find work since being moved from Yunyang County in Chongqing municipality three years ago.

"They lied to us again. They promised us a better life here. We're much worse off," he said, speaking in the thick Sichuan accent of central China.

China's leaders have dwelt on the power and flood control benefits of the biggest Chinese engineering project since Emperor Qinshihuang built the Great Wall more than 2,000 years ago.

Two 700 megawatt generators will fire up in August and 26 turbines are to pump out 18,200 megawatts by 2009 - equivalent of 10 coal-fired power stations using 50 million tonnes of coal a year.

Revolutionary leader Sun Yat-sen first proposed building the dam in 1919, but technical obstacles and social upheaval relegated the plan to the drawing board for 70 years.

Chinese leaders from Mao Zedong to Deng Xiaoping to Jiang Zemin weighed in with support over the years.

There was markedly less fanfare on the weekend. The main players on television were not Chinese leaders but engineers and project heads - who closed the gates with clicks of a computer mouse.

Some gates shut days ago, and water levels had already climbed to 106 metres by Sunday morning. Three of the 22 gates will remain open to guarantee water flow on the Yangtze during the two weeks it takes to fill the reservoir to 135 metres.

Navigation resumes on June 16 on the Yangtze after a break of more than 60 days. The water is to rise further next year, eventually creeping past a sign on the green hills above the dam - "150" - on its way to 175 metres by 2009.