It is not known if there were reports of injuries or arrests.
Tests have shown that at least 615 children out of 731 living in two villages near the Dongling smelter had excessive lead levels in their blood, more than 10 times the level considered safe by Chinese authorities.
| Local officials say they are planning to relocate families living near the plant [AFP]
A total of 166 children have been hospitalised while the rest are being treated at home.
Lead poisoning can damage the nervous and reproductive systems and cause high blood pressure, anaemia and memory loss.
Xinhua said air quality tests done near the smelter showed unusually high levels of lead, although officials say groundwater, surface water, soil and company waste discharge all meet national standards.
The agency quoted a local environmental official as saying lead content in the air near the plant was 6.3 times above that measured at other sites in the region.
Local officials plan to relocate all 581 households living within 500 metres of the factory in the next two years, according to Xinhua, but it was unclear whether the plant had been closed.