A teacher and 24 students at a Mississauga middle school were taken to hospital Monday after feeling ill following a gas leak at the school.

Emergency response services were called in after school staff noticed a gas smell at Allan A. Martin Sr. Public School near Ogden Avenue and Queen Elizabeth Way around 10:45 a.m., a representative from the Peel District School Board told CP24.

The school was then evacuated and firefighters came to the building to investigate the smell. The source was found to be a gas valve in a science lab which had been shut off before the firefighters arrived.

Students went back inside the building around 11:30 a.m. However some students said they were feeling sick, reporting having headaches and feeling nauseated.

An ambulance was called to the school and the students were then taken to hospital as a precaution. They were treated for minor symptoms.

The school board said a note would be sent home with the kids to explain the incident to their parents.

It’s not clear why the gas valve had been left open in the science lab.