Layers of trash are building up in the Yangtze, much of it washed into the river in recent heavy rains and floods, are threatening to jam China's massive Three Gorges Dam, state media said Monday.

The garbage is so thick in parts of China's longest river that people can walk on the surface, the China Daily reported.

Nearly three tonnes of refuse are collected from the world's largest dam every day, but operators are struggling with inadequate manpower and equipment as trash accumulates more quickly because of the floods, the newspaper said.

"The large amount of waste in the dam area could jam the mitre gate (a type of lock gate) of the Three Gorges Dam," Chen Lei, an official with the China Three Gorges Corporation, told the newspaper.

More than 150 million people live upstream from the dam. In several nearby cities, household garbage is dumped directly into the river because municipalities are unequipped for trash disposal.

Chen said 160,000 cubic metres (5.7 million cubic feet) of trash was collected from the dam last year.

The China Three Gorges Corporation spends about 10 million yuan (1.5 million dollars) per year to clear floating waste, the newspaper said.

A 60-centimetre (two-foot) thick layer of garbage covering an area of more than 50,000 square metres (12 acres) began to form in front of the dam when the rainy season started in early July, according to the Hubei Daily.

China considers the 22-billion-dollar Three Gorges Dam a modern wonder. Since its completion in 2008, it has pumped out much-needed hydroelectricity, increased shipping on the Yangtze and helped reduce flooding.

But critics charge the dam has caused ecological damage and increased landslides in the area. About 1.4 million people were displaced by the dam, the construction of which put several heritage sites deep underwater.