Vancouver man Steve Kern was caught up in the celebration of the NBA win as he revelled with the millions of Toronto Raptors fans around Nathan Phillips Square on Monday.

But when four gunshots rang out in Toronto's Downtown, he immediately knew something was wrong. Kern recognized the sound of a handgun because of his extensive career in the military and law enforcement.

"Crack crack crack crack," said Kern, recalling the sound of the shooting that left four people with non-life threatening injuries.

"There were people using fireworks in the audience, but this was definitely shooting."

Then, after a two-second pause, Kern was at the centre of a whirlwind. He remembers people running in every direction and shoving, most trying to get as far away from the gunfire as possible.

That's when Kern's military training kicked in. Making a wedge shape with his arms, he carved his way through the chaos, toward the source of sound.

The crowd's panic stands out in his memory; people screaming and scrambling, dropping bags and grabbing children. Wanting to get above the pandemonium, he climbed onto a large cement block.

That's when he spotted two injured people lying on the ground. One was already being treated by paramedics, the other, a woman, was unattended.

Kern made his way to the woman and began basic first aid. The woman had fallen and had cut her head on the pavement. Kern was soon joined by other volunteers, including an off-duty doctor and a nurse.

Steve Kern, show here on the extreme left, works with volunteers and first responders to help a woman who had fallen and hit her head. (Tijana Martin/Canadian Press)

Kern is now retired after a 35-year law enforcement career that included working as a sheriff, corrections officer and probation officer. He is currently a sergeant-major with the Canadian Armed Forces' 39 Signal Regiment in Vancouver, and a volunteer with St. John Ambulance.

Kern and the team of volunteers eventually helped the injured woman into an ambulance.

"Knowing where the shots were coming from, I was heading in that direction and rolling the dice to get in to help people that needed some help," said Kern.

He said his training is invaluable in emergency situations and urges others to take an interest in first aid.

Kern was in Toronto on his way back from France, where he had been attending a D-day ceremony. Since Monday's shooting, police have arrested three people and recovered two guns.

With files from On the Coast