More than 200 kindergarten students were found to have abnormally high levels of lead in their blood after the school added paint to their food, authorities in northwest China report.

The case highlights long-running food safety concerns in China.

State broadcaster CCTV, citing a police official, said on Tuesday the school in Gansu province added the paint to try to attract more students and increase revenue. CCTV obtained and posted online the full text of an investigation by the province and city.

The Heshi Peixin Kindergarten in Tianshui city bought the paint online and added it while preparing the food, according to CCTV. High levels of lead were found in a three-colour breakfast cake and a sausage dish for dinner.

State-run Jimu News spoke to a parent last week who said that some children attending the centre had been experiencing stomach pain and nausea, and that some of their teeth turned black.

Of the 251 students at the kindergarten, 233 had abnormal lead levels, with 201 receiving hospital treatment, the report said. The World Health Organisation says exposure is “particularly harmful” to young children, including in the development of the central nervous system.

“There is no level of exposure to lead that is known to be without harmful effects,” WHO says.

Dozens of students had levels above the Chinese standard for lead poisoning in children, three other media outlets reported, based on test results shared by parents. The investigation did not provide details of blood tests.

Eight people, including the headmaster, have been detained.