Eleven students from New Asia Middle School in To Kwa Wan were sent to hospital after a gas leak occurred in the school laboratory.
The incident happened around 3.30pm yesterday, when school staff reported that many students were feeling unwell after inhaling gas during a chemistry experiment at noon.
Teachers immediately shut off the gas main and evacuated all students from the laboratory and followed up with an assessment of whether anyone needed medical attention.
Ambulances and a mobile treatment unit were dispatched by the Fire Services Department.
Nine boys and two girls, aged 14 to 17, were found to be experiencing symptoms such as nausea.
All 11 students were taken to Kwong Wah Hospital in Yau Ma Tei.
According to a student, Chan, who was present in the lab, the problem began when students detected an odor after turning on the Bunsen burners for their experiments.
"We soon realized there was a gas leak, with the smell growing stronger."
Chan said he turned off the burner as instructed.
About half the class later complained about feeling unwell.
Another student, Tang, said: "Our teachers told the class to remain in their room until emergency services had addressed the situation."
The secondary three students left school about 30 minutes later than usual.
In a statement, the school's acting principal, Cynthia Lee Wai-man, said that "all affected students are in stable condition."
The school, she said, is also in contact with their parents, and has advised them to monitor their children's condition over the next two days.
An investigation into the cause of the leak is under way.
The Education Bureau has also demanded the school investigate the incident thoroughly, review all lab safety measures, and take steps to prevent a recurrence of the problem.
The bureau will stay in close contact with the school's officials and provide assistance as needed.
This incident marks the second case of students experiencing illness from inhaling gases in a secondary school laboratory over the past academic year.
The authorities are determined to get to the root of the problems and to ensure that robust safety protocols are in place to protect students.
