The stampede broke out early Wednesday during a bathroom break at the elementary school in Puyang County, Xinhua news agency reported.

The injured students were taken to a nearby hospital for medical treatment.

Authorities said they were investigating what triggered the incident.

Overcrowding and poor building design have been blamed for past injuries and crushing deaths at Chinese schools. In 2013, four students died at a school in Hubei province after a collapsed wall caused a stampede there.

The country's deadliest stampede incident in recent years erupted during 2015 New Year festivities, when 36 people died in a crush along Shanghai's riverfront esplanade.

nm/se (AP, dpa, EFE)