Parents and students at Macdonald High School in Sainte-Anne-de-Bellevue on Montreal's West Island were told that their students would be returned home and that classes were cancelled due to "security reasons."

"Students will be returned home by bus," the school wrote on its Facebook page. "We will keep you informed of additional details as events warrant."

Lester B. Pearson School Board communications director Darren Becker said a social media threat was discovered at 8 a.m., but could not say who made the threat or which platform it was posted on.

The school, he said, was closed as a precautionary measure, and that the threat was determined to be "unfounded."

"Our intention is to reopen the school tomorrow," he said. 

Students were not at the school yet when the threat was discovered.