Experts are testing air quality samples taken at a Beijing primary school after some parents of students claimed recently that their children had become ill after exposure to the school's new synthetic playground surface.

Beijing's Xicheng District Education Commission released a statement on Sunday reporting that the China National Environmental Monitoring Center had collected air samples at Beijing No 2 Experimental Primary School's Baiyunlu Campus on Saturday.

Ding Dawei, director of the commission that was in charge of the school's construction, said: "Our priority is the children's health. If the investigation concludes that the playground materials contain toxic chemicals that resulted in health issues, we will track down those responsible."

But a parent surnamed Chen told the Beijing News that the commission should not be involved, suggesting it had a conflict of interest. Only a higher-level department or an independent third-party body should conduct the investigation, Chen was quoted as saying.

"It managed the bidding process for the school's construction, and now is launching a probe into its own work," Chen said of the commission. "It doesn't make sense."

The sampling of air, both inside and outside of 16 classrooms, was observed by the Beijing Jingcheng Notary Office, which the commission had asked to participate as an independent third party to ensure transparency and fairness. Six parents' representatives were invited as well, the commission said.

The investigation was also joined by experts from the city's environmental protection, work safety supervision and medical departments.

Results of the analysis are expected to be announced in a week.

The commission launched the probe after some students' parents reported that their children were suffering from nosebleeds, coughs and rashes, which they believed may have been caused by toxic substances emitted by the playground's new surface.

Ding said parents' complaints were first heard in April about the school's pungent running track, which was installed last summer.

The commission ordered two procedures to neutralize any chemicals in the playground's material and to seal the surface at the time. But more parents reported illnesses in late May, prompting the investigation that was launched on Thursday.

The school has temporarily closed the playground and is allowing students to study at home while the investigation is underway.