A stampede on a stairwell at a middle school in eastern China killed six children and injured 11, state media said Monday.

The stampede occurred Saturday night when hundreds of first-grade students at Tutang Middle School in Jiangxi province's Duchang County swarmed out of their evening classes, the China Daily newspaper said.

Hundreds of students fell over each other in the stairwell between the first and second floors of the three-story building, it said.

Five girls and one boy, aged between 12 and 13, died on their way to hospital, it said. Another 11 students were seriously injured and were being treated at the Jiujiang No. 1 People's Hospital, it said, without giving details.

The report said one student recalled seeing a classmate squatting down to tie their shoelaces on the staircase just before the incident occurred.

The report said teachers climbed drain pipes on the outside of the building to get to the children trapped on the stairwell.

Most of the teachers had been on the first floor grading papers when the stampede occurred and many of the children were unsupervised, it said. The school principle had been detained by local authorities, the paper said.