Parents of students at an elite Chinese secondary school have demanded government action, claiming their children developed health problems from former chemical plants near its new campus, with authorities now investigating the case.

China Central Television (CCTV) reported that 493 students at the Changzhou Foreign Languages School had shown health "abnormalities", ranging from skin rashes to serious illnesses such as leukaemia and lymphoma.

Tests of groundwater on the factory site had shown contaminants far above national standards, the broadcaster said.

"My request is very simple: move to a temporary location," a father who declined to be named told AFP on Thursday. "If the school chooses not to move, I will definitely consider transferring him."

He said his son, a junior high school student, had enlarged lymph nodes which he blamed on the pollution.

Three chemical plants used to be located on a site next to the school premises but closed down and were removed some years ago, before it was built, media reports said.

But there have been no similar reports of illnesses around the neighbouring Changzhou Trina International School, which declined to comment to AFP.

Decades of high-speed economic growth have come at the cost of the environment in China, with local officials often putting development ahead of curbing pollution.

The central government's education and environmental protection ministries have both vowed to investigate the Changzhou case, according to state media.

The local government this week issued a lengthy statement insisting that the site met environmental standards following efforts to clean up the area.

"The experts' group drew a conclusion: the engineering project has already reached the forecast effectiveness for environmental protection. The air quality monitoring completely meets standards," Changzhou city said.

Another parent, who also has a son at the middle school, said they distrusted the local authority.

"We have been disappointed with the credibility of the government again and again. They are neither open nor transparent," she told AFP.

A 17-year-old student, who also boards at the campus, told AFP that several of his classmates had been affected by "toxic air".

"Some of my classmates have very obvious skin reactions and some of them vomited. I live at school too and I can't sleep because of the pungent smell," said the student, who asked not to be identified.

The first students started attending classes at the new school in 2014.

The institution, which includes both junior and senior high schools, had 2,451 students as of mid-March, the Changzhou government statement said. Of the total, four were on sick leave and five were awaiting transfer, it said.

"The school, teaching and studying, are normal," the statement said.