Bishop Tonnos high school was placed in a lockdown Wednesday morning after police were tipped off about a former student who was seen on a bus with a firearm, investigators say.

After investigating, the gun was found to be an imitation, and not real.

Police say they received the report about the man just before 8 a.m.

"The male exited the bus at Bishop Tonnos High School," a police news release reads. "After receiving the above information, Bishop Tonnos High School was immediately placed in lockdown."

Police say they "responded with immediate rapid deployment tactics," and the school was cleared with help from the service's emergency response team.

Investigators say the man was identified by students and staff of the school, and he was then located and arrested off school property.

The 18-year-old former student was in possession of an imitation firearm at the time of his arrest, police say.

Police are still investigating the incident. The 18-year old has been charged with possession of a dangerous weapon and drug possession.

The lockdown at the school was lifted around 9:45 a.m., after first being called at 8:16 a.m. Classes have been cancelled for the day.​

Just before 9:20 a.m., police tweeted that they had completed a search of the inside of the school and everyone inside was safe.

Parents who have a child who was dropped off after the lockdown can pick them up at Resurrection Catholic Cemetery at 252 Gardner Rd. W. in Ancaster, police say.