MONTREAL -- An Ahuntsic high school is under lockdown and now being evacuated after an apparent stabbing that left one victim in hospital.

The "violent altercation" happened in École Secondaire Marie-Anne, at the corner of Sauvé St. and Saint-Laurent Blvd., at around 2:45, Montreal police say.

Two men were involved, both around ages 18 to 20. The incident happened "within a public area in the school," police said.

The victim "likely" suffered lacerations, police said, but they couldn't give a detailed description of the injuries except to say they aren't life-threatening, and he is stable and in hospital.

The suspect left the scene on foot. Police said he's known to them and described him as dark-skinned and wearing a mask. 

As a precaution, police said they are evacuating the classes, though at first, students weren't told what was happening or why.

Police outside Ecole Marie-Anne, Montreal

At around 3 p.m., at least a dozen police cars surrounded the school, said one witness, and students were told to shelter inside.

The lockdown started at about 3:00, said the witness, who didn't want to be named but was in touch with his sister, a student at the school.

The sister said she was sheltering in the school's library with a teacher and a group of other students. They weren't told why. 

At around 3:30 or 3:40, police entered the school with a dog, said the witness, who spoke to CTV News while standing outside the school.

There were no ambulances or fire trucks on scene, nor did the officers have guns drawn, he said. 

The French-language school board hasn't yet responded to requests for information.