BEIJING, Nov 21 (Reuters) - Over a third of China's land is being scoured by serious erosion that is putting its crops and water supply a risk, a three-year nationwide survey has found.

Soil is being washed and blown away not only in remote rural areas, but near mines, factories and even in cities, the official Xinhua agency cited the country's bio-environment security research team saying.

Each year some 4.5 billion tonnes of soil are lost, threatening the country's ability to feed itself.

If the loss continues at this rate, harvests in China's northeastern breadbasket could fall 40 percent in 50 years, adding to erosion costs estimated at 200 billion yuan ($29 billion) in this decade alone.

"China has a more dire situation than India, Japan, the United States, Australia and many other countries suffering from soil erosion," Xinhua quoted the research team saying.

Beijing has long been worried about the desertification of its northern grasslands, and scaled back logging after rain rushing down denuded mountainsides caused massive flooding along the Yangtze in the late 1990s.

But around 1.6 million square km of land are still being degraded by water erosion, with almost every river basin affected. Another 2.0 million square km are under attack from wind, the report said. The survey was the largest on soil conservation since the Communist Party took control of China in 1949. ($1=6.835 Yuan) (Reporting by Emma Graham-Harrison)

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