More than 400 students at the middle school in Gansu province's Tianshui city took part in the combined fire and air raid drill on Friday when the artificially generated smoke surged out of control, the official Xinhua news agency reported.
"Many students began to cough and vomit after inhaling the smoke," the report quoted the local government as saying. Officials could not be immediately reached for comment on Sunday and the report did not say what type of smoke was used.