According to police, four people were injured during a shootout in Toronto during a tight rally around the Toronto Raptors basketball team's victory.
Thousands of sports enthusiasts were massed in downtown, at Nathan Phillips Square, when gunshots rang out, making many runners looking for a blanket.
The event was only briefly interrupted by officials who calmed the crowd.
Three people were arrested. The authorities have asked the public to send pictures to facilitate their investigation.
Police tweeted that none of the victims had sustained life-threatening injuriesalthough two were seriously injured.
They also claimed to have recovered two firearms from the scene.
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It is estimated that nearly two million spectators gathered Monday in downtown Toronto for a parade in tribute to the basketball team.
The Raptors, the only franchise of the National Basketball Association in Canada, won the championship final against the Golden State Warriors last Thursday – the first Canadian team to win the US title.
In the middle of the afternoon, thousands of partygoers gathered to attend the closing ceremony of the event with players and dignitaries, including Prime Minister Justin Trudeau.
Mr. Trudeau then tweeted that he was hoping for a "speedy recovery" for the wounded.
"We will not let this act of violence undermine the spirit of the parade today," he said.
Toronto Mayor John Tory said he was "disappointed" that the event was marked by gun violence.
Canadian sports fans enjoyed the victory of the Toronto Raptors, the league's first championship victory in 24 years of history.
The team's players were transported along the parade route into five double-decker buses where they were welcomed into Raptors shirts and jerseys. The crowd dispersed without further incident in the late afternoon.
Mr. Tory proclaimed July 17 as "North Day" by using the slogan of the "We North" team – to commemorate the historic season.