CALGARY -- Alberta's police watchdog is asking for witnesses of a Saturday incident in downtown Calgary during which a police member fired at a vehicle officers believed was headed for a military parade.

Police attending the Freedom of the City parade at 3 p.m. first noticed a suspicious vehicle near the intersection of 6 Street and 8 Avenue SW trying to drive around one of the barriers.

"As we were marching from City Hall to Mewata Armoury there was a law enforcement incident. We paused the parade briefly to allow the police to deal with the situation and we carried on with our parade,” said Lt.-Col. Peter Boyle, commanding officer of the 41 Service Battalion. 

Calgary Police Service officers tried to block the black 2008 Toyota Corolla, but said the vehicle made a U-turn and attempted to flee the scene.

"The officer who had attempted to intercept the vehicle, and two other additional officers, approached the vehicle and began to issue commands to the driver. The driver failed to comply and first backed up, then drove forward, westbound, on the sidewalk in the direction of where two CPS members were standing," the police service said in a statement.

That's when one of the CPS officers, a 12-year member, fired three shots.

The suspects continued to try to flee north, but crashed into a van that was being driven by a bystander.

Bonita Vance was in the area when the incident took place. She told CTV News Calgary she saw the suspects' vehicle, a black car, speeding down the road.

"It was trying to beat the red light, but hit the van instead. I saw the impact, I saw his airbag go off and that was it."

Police say both people in the black car tried to run away, but were quickly arrested.

The 21-year-old man driving was shot in the left arm and the passenger, a 28-year-old woman, took a bullet in the left thigh, police said. Both were treated in hospital. The woman has since been released.

Calgary police say no pedestrians were injured, nor was the driver of the van.

Charges had not been laid as of Sunday afternoon, as the driver is recovering from surgery related to his injuries.

The Alberta Serious Incident Response Team, which investigates officer-involved shootings, has taken over.

Local forces are working with national security partners in the investigation, but say there is no known link to terrorism.

The investigation is on-going. ASIRT is asking those who witnessed the scene or have video of it to call 403-592-4306.