École secondaire Mont-Bleu in Gatineau, Que., is closed Tuesday and could remain closed for several more days after windows were broken and a fire was started overnight.
Gatineau police told Radio-Canada the vandalism happened overnight Monday into Tuesday.
Most of the damage was done inside the building, police added.
No suspects have been identified and an investigation is ongoing, police said.
Classes are suspended Tuesday and staff are working remotely, the school service centre said. It said it hoped students could return on Thursday.
The school moved to the Asticou Centre in December 2018 after its building was damaged by lightning as a tornado-producing storm tore though the National Capital Region that September.
Classes had begun for this school year on Aug. 31.