TORONTO — A shooting that sparked a stampede at a massive rally celebrating the Raptors' historic NBA title highlighted the challenges of organizing a large celebratory event in a sprawling metropolis such as Toronto, authorities said Monday.

Officials had to balance the fan experience with safety concerns as they planned for a kilometres-long victory parade and ensuing public party, said city spokesman Brad Ross. The biggest logistical challenge, he said, was the estimated two million fans who turned out — about a million of which were gathered at the rally outside city hall.

"How do you keep back more than a million people on the parade, when really this is all about a celebration and not security," Ross said. "You try to make the players and the team accessible because the fans want to thank the players and players want to thank the fans."

Barriers had been set up along parts of the parade route, but fans hopped those fences in many areas, crowding the floats that carried the team and other dignitaries. The parade itself was significantly behind schedule, leaving fans packed into Nathan Phillips Square — the site of the ensuing rally — waiting hours to see the champions.

The public party at the square, once it finally got underway, was briefly suspended due to the shooting before carrying on even as fans on one end pushed and shoved while scrambling for cover. Some parents were separated from their children, other fans lost backpacks and purses and several screamed amid the chaos.

Police said four people suffered injuries related to the shooting. Three people were arrested and two firearms were recovered, police said.

Toronto police Chief Mark Saunders defended the city's role in the massive Raptors' party.

"We're not going to turn it in to a security event, we're not going to transition to that, we didn't feel there was a need for that," Saunders told reporters after the celebration. "This is a once-in-a-lifetime for so many people."

Ross said the city had begun planning for the parade while the Raptors played the Golden State Warriors in the NBA Finals, using experience the team's owners — Maple Leaf Sports and Entertainment — and police had gleaned from the numerous events at Jurassic Park, the fanzone outside the Raptors' arena.

Security during the parade and rally was tight around the team, Ross said, noting that Prime Minister Justin Trudeau and other high-profile guests such as Ontario Premier Doug Ford and Toronto Mayor John Tory were all on stage when the shooting occurred.

"Given the time we had to pull this together and the size of the crowd, I'd say it was a special event overall," Ross said. "There are things that are going to happen you can't control for, but that's why we had such a heavy police and security presence."

Tory said he wanted to thank the Raptor fans who showed up and celebrated peacefully as well as the police for their efforts after the "unfortunate" shooting.

"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," he said in a statement.

Toronto's transit commission closed down three nearby subway stations due to overcrowding as fans congregated downtown for the festivities. It also cut power to the overhead streetcar lines nearby at one point "due to unsafe behaviour and people climbing TTC infrastructure."

Toronto EMS spokeswoman Kim McKinnon said besides two people taken to a trauma centre with gunshot wounds, paramedics transported about 10 people to hospital, most with minor heat-related illnesses.

"This is a very, very large crowd, so this is not out of the ordinary for us," McKinnon said.

Toronto Fire district chief Stephan Powell said firefighters dealt with about a dozen calls for dehydration in the square.