Four people were shot at a rally celebrating the Toronto Raptors' first NBA championship on Monday afternoon, according to police, amid a celebration that saw thousands of fans crowd into the city's downtown core.

Police took three people into custody and recovered two firearms, Toronto Police Chief Mark Saunders told reporters.

Two people were arrested in connection with one shooting, Saunders said, while the third was arrested in connection with the other. He did not go into further details.

The shootings happened around 3:45 p.m. ET, at Bay and Albert streets — near city hall and Nathan Phillips Square where a rally capping off a victory parade was coming to a close.

The four victims suffered non life-threatening injuries and the arrests were done "incredibly quickly," Saunders said.

Toronto Mayor John Tory, who was on the stage in the square when the shooting happened, thanked police in a statement later for their quick response to the incident.

"It is disappointing and I'm sure a source of anger for more than just me that anyone would carry a gun and discharge it at what was otherwise a joyous celebration."

Tory also commended the millions of people who celebrated "our beloved Raptors" peacefully.

Saunders appealed to witnesses to come forward to help police with the investigations. Police estimate that more than one million people lined the parade route and attended the rally.

Saunders said police wanted to keep the day "celebratory," despite the violence.

"In this particular case, because of the quick apprehensions and the fact we were able to control the situation to the best of our abilities in a short period of time, the event was able to go on," he said.

WARNING: Video contains coarse language. A video captures people running after a shooting during the Raptors championship rally near Nathan Phillips Square. 0:37

Saunders was asked if police were prepared for the large number of people at the parade given that at several points there weren't any barricades set up to keep the crowds off the route. The crowds seemed to slow down the parade, which arrived at Nathan Phillips Square three hours later than scheduled.

"This is a once in a lifetime for so many people," Saunders said.

"It took a little longer, but I don't think people were interested in the timelines."

Video taken by CBC News reporters at the scene showed people scattering from the area after the gunfire rang out.

I hope all those injured in today’s shooting have a speedy recovery, and I’d like to thank the Toronto Police for acting so quickly. We won’t let this act of violence take away from the spirit of today's parade. —@JustinTrudeau

Matt Devlin, the master of ceremonies for the rally paused briefly to let the crowd know there was an emergency situation and to advise revellers to stay calm.

"This is about love, it's about rejoicing," he told the people gathered in and around city hall's public square. He urged fans to stay strong and "stay together."

Raptors broadcaster Matt Devlin interrupts championship ceremony to calm spectators after gunshots rang out near the festivities. 2:03

Prime Minister Justin Trudeau, Ontario Premier Doug Ford, Tory and team executives and players remained on the scene.

Within moments, the speeches continued.

Devlin's reaction prompted praise from at least one police officer.

"Amazing job ... taking over the mic and keeping all under control during police response. You my sir settling the crowd saved (many) injuries, great work!" the officer tweeted.

"I had ... to make sure everybody was calm, because you don't want that to trigger something else. Hopefully I was able to do that in some small way," said the Syracuse, N.Y., native, also known as Matty D.

"I felt like I wanted to keep talking, because the longer that I talked, the calmer people would be. And hopefully that's the case."

This was the scene as people panicked and ran from Nathan Philips Square. <a href="https://t.co/9UtSoHuRoo">pic.twitter.com/9UtSoHuRoo</a> —@LindaWardCBC And again. People running away from the right side. Not sure what’s going on <a href="https://t.co/1fEoGoaVMl">pic.twitter.com/1fEoGoaVMl</a> —@fitzpatrick_m

Minister of Border Security and Organized Crime Reduction Bill Blair, who also served as chief of police in Toronto, said in such situations, the priority is to keep everyone safe while also securing the scene and preserving potential evidence, as well as apprehending suspects.

Such occurrences "take away everyone's sense of safety and security," he told CBC's Power & Politics.

"Why would anybody bring a weapon to an event like that? And then use it in a public space. It's an offence that victimizes the entire city."