Thirty-four middle school students fell ill after eating at their school canteen on Tuesday in southwest China's Guizhou Province, school authorities said Wednesday.

The students, aged 13 to 15, experienced stomachaches and nausea at around 10 p.m. and were sent to a local clinic for treatment, said Zhang Qifu, principal of Maoshi Village School in Tongzi County.

Eleven of the cases were serious, and those students were transferred to the county hospital on Wednesday morning, said Zhang.

"All the students are in stable condition now," he said.

The principal said he suspects they fell ill after eating moon cakes served at the canteen, as more than a week has passed since the traditional Moon Festival and the cakes could have been stale.

The county government has launched an investigation.