Nine people were injured when gunfire rang out as fans celebrated the Denver Nuggets first-ever NBA championship win on Monday night.
Three of those hurt in the shooting outside the arena were in a critical condition, police said. The others had non-life-threatening injuries.
A suspect was also shot and was in police custody, investigators said.
Police said they believe "multiple shots were fired during an altercation involving several individuals".
The shooting happened on Market Street, close to Ball Arena, where the city's basketball team, the Denver Nuggets, beat Miami Heat 94-89 on Monday night.
Police said they believe "multiple shots were fired during an altercation involving several individuals".
Denver Police Department spokesperson Doug Schepman told CBS Colorado the shooting happened about three-and-a-half hours after the game.
Crowds had dispersed, leaving only a smaller number of people in the area when gunfire rang out.
Footage of the scene earlier showed thousands of fans flooding streets and setting off fireworks after the Nuggets' historic win.
According to the organisation that monitors mass shootings in the US, the shooting in Denver is the 291st this year.
The Gun Violence Archive defines a mass shooting as an incident in which four or more people are killed or injured. Their figures include shootings that happen in homes and in public places.
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