MONTREAL -- Massey-Vanier High School in Cowansville was locked down on Thursday after a student said she heard another group of students talking about bringing a gun to school.

A parent at 8:40 a.m. notified administrators that her daughter overheard three students mention the possibility of bringing a gun to school, said Julie Edwards, the school principal.

"She didn't know if it was a joke, but it bothered her, so the mother called, and from there, we follow our procedures," she said. "When you get a call like that, you have to err on the side of caution."

Teachers ushered students into classrooms and locked the doors. For two hours, students sat on the floor, unsure of what was going on. Provincial police were called to investigate. Officers were also dispatched to other locations, according to the Surete du Quebec.

Rumours that a gunman had entered the school circulated, disturbing parents who had no way to find out what was happening inside the school.

"It was terrifying. ... You know how these things can go down, and you don't ever want that to happen," one parent tearfully told CTV News.

Three students were later detained and questioned, but no weapons were found, an SQ spokesperson said.

The Commission scolaire du Val-des-Cerfs, which oversees the French portion of the school, confirmed on its Facebook page that one of the students stopped by police was not on school grounds.

"Professional services will be on hand to support students and staff," the school board added. "The rest of the day will continue on schedule. However, parents wishing to pick up their child can go to Gates 24 and 25 without entering the school."

The Eastern Townships School Board, which oversees the English part of the school, notes the lockdown was a "preventative measure taken to ensure the security and safety of our students and staff" due to a perceived threat outside the school.

"We can now assure parents that all students and staff are safe and secure, and the authorities are on site managing the situation," it stated on Facebook.