A joint investigation team was formed on Monday to look into pollution-related illnesses among students at Changzhou Foreign Language School in Jiangsu province.

The team was setup by the Ministry of Environmental Protection and the provincial government.

Of 641 students examined at hospitals, 493 have been diagnosed with diseases and conditions related to pollution, including dermatitis, bronchitis and blood abnormalities. Some were found to have leukemia and lymphoma.

The investigation team has traveled to Changzhou and will release its findings to the public as soon as possible. The Changzhou government has also formed an investigation team.

According to the Changzhou authorities, parents and the school hired professional testing organizations in late March to check the quality of indoor air, soil and groundwater. The results showed that all met national standards.

The school said that all of its 2,451 students - except for four asking to be transferred, three calling in sick and one on leave of absence - have attended classes regularly. Only three of its 210 teachers have called in sick.

A notice issued by the Changzhou government on Monday said: "The supervision of the public is welcomed. We'll investigate carefully and deal with the problem according to the law."

However, many parents have doubts over environmental conditions at the school and have forbidden their children from eating any food or drinking water that it provides.

Wan Ling, the mother of a 13-year-old student, said: "I now send lunch to my son every working day. ... So many students cannot get sick at the same time without a reason."