Parents of students at a primary school in Wuhan, Hubei province, say their children were sickened by fumes emitted by a new synthetic running track and that an inappropriate standard was used to test the material.
The incident mirrors a similar one at schools in several provinces in 2016.
Samples of the track at Canglong No 2 Primary School in Wuhan were immediately tested and found to meet national standards, the publicity office of the city's Jiangxia district said on Monday, adding that testing reports were issued by two organizations.
But some parents say those results are misleading because an outdated testing standard was used.
In May this year, responding to the 2016 incident, the Ministry of Education released new standards, which are mandatory but won't take effect until Nov 1. They replace standards adopted in 2011.
China Newsweek cited unnamed parents on Sunday as saying the testing this time was based on the older standard, which contractors insisted upon using even though the parents demanded that the updated standard be used.
Earlier this month, parents of students attending Canglong complained that fumes given off by the newly laid school running tracks had sickened students, who had symptoms such as vomiting and nosebleeds.
Local education authorities invited the Hubei Institute of Quality Supervision and Inspection, along with Ingeer Certification Assessment Services in Shanghai, to examine samples taken from the track and basketball courts, Jiangxia district said.
The Shanghai organization was invited at the request of parents who said they didn't trust the local examiners. Parents' representatives were present when samples were taken.
The examination results from the two organizations show that the chemical levels in the school's running tracks and basketball courts "meet national standards", the statement said.
Education authorities asked schoolteachers and parents to take any sick children to the hospital for medical exams. It was determined that 34 of the 38 students had normal blood, while four students had slightly high levels of blood proteins, caused by a viral infection, the statement said.
The district government organized a thorough cleaning of school classrooms and playgrounds over the weekend. Green plants that can absorb toxic fumes were placed in every classroom and public area.
After an investment of more than 70 million yuan ($10.2 million) over the last two years, the school prepared for the start of a new semester this month. Around 1,200 students were expected to enroll.
Parents reached by China Daily on Monday declined to comment on the statement.
According to China Newsweek, more than 130 students had experienced nosebleeds, vomiting or skin allergies as of Friday. Their parents were quoted as saying that the running tracks, which were built in July, emitted strong odors, and that odors were present in classrooms when the new semester began.
Similar complaints were widely reported in 2016, when media cited a number of cases in which parents claimed their children suffered nosebleeds after tracks were laid in several provinces, including Jiangsu and Guangdong.
As a result, the ministry ordered schools across the country to destroy all substandard tracks and began drafting the new national standard on synthetic tracks.
