'When I took my sons to hospital, the doctor asked if we lived near a heavy metal plant,' said Lei from Hengjiang village. 'We suspected the manganese smelter that opened last year was to blame.'

Another villager said: 'Whenever the plant is operational, we can see thick smoke and dust in the air.'

Authorities shut down Wugang Manganese Smelting Plant on Aug 13.

Police have detained two of its executives, Deng Qingguo and Yi Jianhua, on suspicion of 'causing severe environment pollution', but general manager Liu Zhongwu is still at large.

The plant opened in May 2008 without the approval of the local environment protection bureau, said Huang Wenbin, deputy environment chief in Wugang city.

Within a radius of 500 meters from the plant is a primary school, a middle school and a kindergarten.

'We used to recruit several hundred children every year but parents have stopped sending their children here this summer,' said a kindergarten teacher. 'Who knows, maybe our classrooms will all be empty when the new term begins next month.'

In a similar incident in northwest China's Shaanxi province, discharges from a zinc and lead smelter left 851 children ill with excessive lead in the blood. All the children live within 500 metres of the plant.