More than 60 students were injured when hundreds of balloons exploded at a school in northwest China's Gansu province, state media reported.
The accident happened at the opening ceremony of a sports event at a school in the provincial capital, Lanzhou.
Over 1,500 small balloons filled with hydrogen caught fire and exploded, burning dozens of students.
Xinhua news agency said that at least 64 students were taken to two different hospitals in Lanzhou.
Most were suffering from burns to the face, hands and back, the agency said, citing doctors.
An investigation into the cause of the accident is underway.