Nearly 30,000 people in central China on Tuesday have been mobilized to guard a riverside city as the biggest flood peak in nine years is roaring down the Yangtze River, the country's largest waterway.

Tens of thousands of people have been summoned to stand guard to stop flood waters breaching dikes in Jingzhou city, Hubei province. Authorities declared more than 620 kms of river banks as risky along the Yangtze and its tributaries in the city.

"The priority is to monitor dike breaching. All related government departments should make contingency plans and stay vigilant," according to a statement issued by the municipal government.

Jingzhou, with a population of 6.45 million, lies downstream of the Three Gorges Dam, the world's largest water hydropower project. The dam's operators said the biggest flood peak since its establishment in 2003 would pass through it at 8 p.m. Tuesday.

Water inflow into the dam area reached 71,200 cubic meters per second -- stronger than the devastating 1954 and 1998 Yangtze floods -- but the dam managed to reduce the force to just 43,000 cubic meters per second, the operators said.

Built to tame annual Yantze floods and generate power, the dam is capable of holding 22 billion cubic meters of water.

The 3,219-km-long Yangtze that cuts through China from the Qinghai-Tibetan plateau in the west to the East China Sea, killed 33,000 people in its 1954 flood and 1,562 in the 1998 flood.