A 17-year-old student was in hospital with life-threatening injuries Monday after being stabbed inside his high school in Toronto's east end.

Officers responded to reports of a stabbing at Birchmount Park Collegiate just after 3 p.m., Toronto police Insp. Craig Young told reporters at the scene, where a large police presence remained into the evening.

Upon arrival, police found a male Grade 12 student in the school's office suffering from an apparent stab wound and "immediately commenced life-saving measures for an extended period of time," Young said. Toronto Paramedic Services then arrived and transported the victim to hospital, where he remained in critical condition late Monday.

"I cannot share any suspect information with you at this time," said Young. "I want you to know that we do not believe that there are any concerns for public safety at this point in time."

Police officers were still on scene clearing the school room-by-room and helping with the safe dismissal of students from their classrooms hours after a lockdown at the school was lifted. Officers could be seen operating a drone flying above the school.

Students were being dismissed in a parking lot at the east side of the school, where they could be seen being picked up by parents or getting into cars in groups. Some students lingered in groups outside the school and a large area in front of the school was blocked off by police tape.

Young said Toronto police detectives were at the school and elsewhere following up on leads in the case. He added that some students in the school "deemed to have been a witness or involved in the incident in any way" were being interviewed by police.

Social workers were on site supporting students and staff impacted by the stabbing and will be available on Tuesday as well, said Toronto District School Board spokesperson Ryan Bird. The TDSB confirmed in a tweet that the school will be open on Tuesday.

"Our heart goes out to the victim in this and it is our hope that he makes a speedy recovery," Bird told reporters at the scene. "It is a larger school, and so when something like this happens just before dismissal, it can be chaotic."

The incident is the second stabbing to take place at Birchmount Park Collegiate this year, after a 14-year-old student was stabbed outside the high school in April. The student was taken to hospital by paramedics but not seriously injured.

The stabbing also comes two weeks after a shooting outside Woburn Collegiate Institute, another high school in the city's east end, that left one student dead and another injured.

"Schools deserve to be a safe place to learn and work," said Bird.

"While the TDSB plays an important role in what that solution may be, I do think we need help from other levels of government and community partners. This is not something TDSB can do alone," he said.

After being dismissed from his classroom after two-and-a-half hours in lockdown, Kkid Kkid, a Grade 12 student at Birchmount Park Collegiate, said students were given little information and told to stay in place until police arrived.

"It's a great school. These sort of things happen but there's great teachers, great staff," he said. "Hopefully these events don't allow people to just categorize the school into a bad place."