Ontario’s Special Investigations Unit is probing a police-involved shooting on a Toronto streetcar early Saturday morning that left a young man dead.

Bystanders at the scene say they saw police surround a stopped streetcar on Dundas Street near Grace Street just after midnight. Witnesses say police had their guns drawn and asked a man on board to drop a knife.

A single officer opened fire a short time later, witnesses report.

Video footage shows the streetcar stopped in its tracks as bystanders quickly back away from the unfolding situation.

At the door of the streetcar, a man in light-coloured pants can be seen standing, as a police officer runs around the side of the vehicle and draws his weapon. At that moment, shots are heard being fired.

Martin Baron was returning from a late dinner when he heard police shouting.

“We hear the cops yelling at the top of their lungs, ‘drop the knife, drop the knife,’ and then I could see through the window of the streetcar just behind the driver’s seat, a guy standing up -- quite clearly had a knife, you could see the knife.”

Baron said he saw the man being tasered after the shots were fired.

The man in his 20s had CPR performed on him before he was rushed to hospital with gunshot wounds. He was pronounced dead a short time later, according to the SIU.

It’s not clear how many times the man was shot or why police elected to use deadly force.

The driver and all passengers were off the streetcar at the time of the incident.

“TPS were called to investigate a male on a TTC streetcar travelling west on Dundas Street and we understand that there was an interaction involving the male and officers and as part of that interaction a police firearm was discharged and the male was struck,” SIU spokesperson Jasbir Brar told reporters at the scene Saturday morning. “He was transported to St. Michael’s Hospital and he was later pronounced deceased at the hospital.”

The SIU has assigned six investigators and two forensic investigators to the case.

The SIU investigates incidents involving police where there has been a death, serious injury or allegations of sexual assault.