About 10 percent of China's farmland contains excessive levels of heavy metals due to contaminated water and poisonous waste seeping into the soil, state media said Monday, citing a government survey.

Pollution from heavy metals such as lead, mercury and cancer-causing cadmium is often blamed for poisoning entire villages and crop-growing land in China as factory bosses flout environmental laws and farmers use toxic fertilisers.

The report in the Southern Metropolis Daily said the survey organised by the environmental protection ministry found about 10 percent of farmland had "striking problems of heavy metal levels exceeding (official) limits".

"Heavy metal pollution incidents have occurred repeatedly in recent years," Wan Bentai, chief engineer at the ministry, was quoted saying.

"From January to August alone there were 11 cases -- nine involving lead in the blood."

The report did not say what level of heavy metals was considered excessive or how much of the country's agricultural land contained toxins.

China's rapid industrialisation over the past 30 years has enabled it to become the world's number-two economy.

But the focus on growth, combined with lax environmental protection, has saddled the country with some of the world's worst water and air pollution that has triggered numerous public health scares and a growing number of protests.

Thousands of residents in the northeastern city of Dalian protested in August against a factory that made paraxylene, a flammable carcinogenic liquid used in the production of polyester films and fabrics.

In September, more than 500 residents living near a plant making solar panels protested for three days in the eastern city of Haining, forcing authorities to temporarily shut the factory.

In the same month, authorities in Shanghai halted production at most of the city's lead battery plants after 32 children living near two plants using lead in production reportedly were found to have excessive lead in their blood.