Police say four people have been injured and three others are in custody following a shooting in Nathan Phillips Square during the Raptors NBA Championship fan rally.

Shots were heard near Bay and Albert Streets at the south east corner of the square shortly before 4 p.m.

The injuries of all victims are serious, but non-life threatening.

Three suspects were arrested soon after the shooting.

One suspect was arrested on the south side of Queen Street by Albert Street. Several officers reportedly immobilized the suspect and seized a pistol.

Two other suspects were also arrested and a second firearm was recovered.

Police Chief Mark Saunders says the arrests were made moments after the shooting.

“With all the resources that were here, the apprehensions were done incredibly quickly after the incident itself,” he said, adding that the investigation is in very early stages. “It’s really early and we are trying to see what roles, if any, the people we apprehended have in this case. We do have people arrested with firearms and that’s the start of the investigation.”

Saunders added that the incident did not happen in a”vacuum” and appealed to witnesses to come forward, saying there were over a million people present.

Mayor John Tory released a statement thanking Toronto Police for their quick response to “today’s most unfortunate shooting after an otherwise spectacularly successful day.”

“It is disappointing and I’m sure a source of anger for more than just me that anyone would carry a gun and discharge at what was otherwise a joyous celebration,” said Tory.

As the incident unfolded, Raptors play-by-play announcer Matt Devlin, speaking from the stage, confirmed there was an emergency taking place and urged fans to stay calm as the festivities were briefly suspended.

The events quickly resumed even as dozens of fans ran in several directions at one end of the square.

Eye witnesses said word of the shooting sent a section of the crowd into a stampede, with people screaming and hiding in nearby bushes. They say children in strollers were bowled over as frantic parents tried to shield them.

Some in the crowd said they hadn’t heard any shots but rushed from the area as others panicked.

Mike Mudidi, a fan attending the event, said he was enjoying the celebrations when he heard screams behind him that someone had pulled out a gun. He says he grabbed his buddies’ hands and ran.

Some who stayed behind huddled near pillars in Nathan Phillips Square even as the team and several dignitaries — including Prime Minister Justin Trudeau — remained on stage. The ceremony wrapped up a short time later.

Several people were reportedly transported to hospital including a police officer who was caught in the stampede.

Saunders said there was no word on how many suffered injuries in the aftermath of the shooting.

Panic spread to the Eaton Centre as the shots were heard through the Albert Street entrance and frightened people were seen running in the mall and outside, at Yonge-Dundas Square.

Several people rushed to take shelter in Citytv’s lobby, behind Yonge-Dundas Square, amid the moments of chaos.

One witness said it was her first time coming to a parade like this and she was terrified when she saw people running.

“I was running for my life. Everybody was trying to get somewhere safe and it was just crazy,” she said.

An investigation is ongoing.

Earlier in the day multiple people were injured, including at least one seriously, after a pair of stabbings at the Eaton Centre.