More than 150 students are in hospital, 10 of them in a critical condition, after inhaling smoke from smoke guns used during a fire drill on Friday at their school in northwest China's Gansu Province.

The 165 students of the junior middle school in Tianshui City are at four hospitals, with 90 of them under less intense medical observation, according to a statement issued by the Tianshui government on Monday.

A Sunday statement said only nine students had been hospitalized after the incident.

The government said 412 students participated in the drill, which used smoke guns to simulate fire. Many of them began to cough and vomit after inhaling the smoke.

An expert panel dispatched by the National Health and Family Planning Commission arrived in Tianshi early on Monday to assist in the treatment.