Shanghai said Friday it had ordered the temporary closure of two plants, including a unit of US Fortune 500 company Johnson Controls, over fears they may be causing lead poisoning in children. \"A small amount of children living in the Kangqiao area in eastern Shanghai were found to have excessive levels of lead in their blood in early September,\" the Shanghai Environmental Protection Bureau said in a statement. The agency said an initial investigation found that battery maker Shanghai Johnson Controls International Battery Co. -- a unit of the New York-listed Johnson Controls -- had been emitting dust and smoke containing lead. Another plant called Shanghai Xinmingyuan Auto Accessories Co. had been found using lead in production without proper approval, and both factories had subsequently been ordered to shut down, it added. Johnson Controls, an industrial giant that ranked 76th on this year\'s Fortune 500 list, said it believed its plant was not the source of the problem but that it was cooperating with the city government. \"We are working with the government to understand and address these issues. However, we have no reason to believe we are the source of the issue,\" it said in a statement to AFP. Johnson Controls said the plant\'s lead emission average was one-seventh of China\'s national standard, while the discharge through wastewater was one-tenth the national requirement. Xinmingyuan Auto Accessories refused to comment. Excessive levels of lead in the blood are considered hazardous, particularly to children, who can experience stunted growth and mental retardation. The environmental bureau did not say how many children were affected by the pollution leak but the Shanghai Daily, a newspaper controlled by the local government, said that 25 children in the area were found with high lead levels. China\'s rapid industrialisation over the past 30 years has enabled it to become the world\'s number two economy, but has also left it with widespread environmental damage that has triggered numerous public health scares. Earlier this year, authorities in the eastern province of Zhejiang detained 74 people and suspended work at hundreds of factories after 172 people -- including 53 children -- fell ill due to lead poisoning. And in 2009, local smelting plants were found responsible for nearly 1,000 children testing positive for lead poisoning in the central province of Henan.