At least 26 villagers have died from cadmium poisoning and hundreds more fallen ill since 2009 near a disused factory in central China, local media said Wednesday, underscoring the country's mounting pollution challenge.

Soil samples from Shuangqiao in Hunan province contained 300 times authorised cadmium levels and excess amounts were found in 500 of 3,000 villagers tested by health authorities, the China Youth Daily said.

It said 26 people had died as a result of cadmium exposure in the last four years, eight of them under 60 and 20 of them from cancer, while children in the village were born with deformities.

A major chemical plant operated in the village until 2009, and a "huge" industrial waste pile remains in the factory grounds, as does "an odour that will not go away", the paper said.

It described the situation as "one of the country's 10 biggest pollution incidents".

Cadmium is highly toxic and exposure to the metal "is known to cause cancer", according to the US Department of Labor.

China is grappling with severe environmental degradation inflicted by decades of breakneck economic growth, and communities have protested industrial projects they fear will harm their hometowns or their health.

Amid growing concern about ground pollution, China recently carried out a five-year nationwide soil survey costing one billion yuan ($160 million).

But early this year it declared the findings a "state secret", underscoring the sensitivity around the issue.

The environment ministry this year acknowledged for the first time the existence of "cancer villages", years after domestic media reported on more than 100 polluted rural areas with higher incidences of the disease.