A total of 43 Canadians, including 35 children and eight adults, are hospitalized Monday due to a carbon monoxide leak in an elementary school in Montreal, Canada, according to local media CTV.

The 35 pupils and eight staff members at Ecole des Decouvreurs in LaSalle, a school of some 270 pupils, suddenly started falling ill about 11:30 a.m. Monday. Ambulances were sent to the school to treat and evaluate sick people at the scene.

Those hospitalized, who are in stable condition and under observation, complained of symptoms including dizziness and nausea.

The problem stems from the school's heating system, which released deadly carbon monoxide into the building. All people were evacuated from the building and fire crews would ventilate the structure before workers repair the heating system.