Chinese state media say more than 150 students fell ill in northwest China after breathing in smoke from a mock air defense evacuation drill.

The official Xinhua News Agency says the Civil Air Defense Office of Tianshui city in Gansu province and the Yifu Experimental Middle School jointly organized a drill Friday. To make the drill more realistic, they used smoke, but the volume generated was too large.

The Gansu Daily reported Sunday that more than 150 students had been treated, with complaints including coughing, vomiting, fever and bleeding in the digestive tract. It said 142 were still under observation Saturday and nine were in serious condition.

Cities across China have sounded air raid alarms this weekend as part of an annual education day to raise awareness of national defense.