A mad rush to the playground turned into a stampede that left dozens of elementary school children injured in western China on Monday, state media and officials said.

Students at the No. 5 Elementary School in Aksu city, Xinjiang, were rushing downstairs for after-class exercises around noon when some students fell, the official Xinhua News Agency said. The report said that other students then pushed to squeeze through the narrow stairway, trampling on those that had fallen.

Xinhua put the numbers injured at nearly 100 while an official with the Aksu government's propaganda office said more than 40 were injured and were being treated in hospital. No deaths were reported.

The official, who only gave his surname, Lu, said an investigation was under way. It was unclear whether teachers or other adults were present during the incident.

School safety in China came under scrutiny earlier this year when a string of stabbings around the country killed and injured dozens of schoolchildren. The attacks prompted Chinese authorities to tighten security at schools. Police and guards were posted at entrances and video surveillance and intruder alarms installed on some school premises.