A day after 41 primary school students were injured in a stampede in Aksu, Xinjiang Uyghur Autonomous Region, there was no clear explanation about what caused Monday's incident.

About 100 students tripped and fell down a stairs inside the No. 5 Primary School as they rushed from the second floor of the four-story building to reach the playground to exercise. The guardrail was bent out of shape, according to the Xinhua News Agency.

A student who was critically injured during the episode was still in the inten-sive care unit Tuesday but was stable. Six other severely injured students were in stable condition, while 34 others who were slightly injured were still in a hospital for observation, Lu Guoping, the Aksu city spokesman, told the Global Times Tuesday. Some 123 students were taken to Aksu's No. 1 People's Hospital and 41 were admitted.

Normal classes were held Tuesday for the school's 1,900 students. However, it was still unclear what caused the stampede. "As far as I know, there is no plan to investigate what or whom caused the incident," Lu said.

The Ministry of Education issued a circular Tuesday calling on schools nationwide to impose better safety measures and to tighten security inspection.

It said that teachers should stand near stairwells when students are leaving, and that they stagger class breaks so that a limited number of students are outside classrooms at a given time.