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A Denver motorcycle expo turned deadly Saturday when a melee broke out between two rival biker gangs, police and sources said.

One person was fatally shot and three others were wounded by gunfire at the Colorado Motorcycle Expo, police said. The incident happened just before 1 p.m. local time (3 p.m. ET).

One person was stabbed and three others suffered lesser injuries likely suffered in the fistfight, Denver Police Chief Robert White said. There have been no arrests, police said.

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"We've been interviewing several witnesses and we do have one person of interest," White said.

White said the incident began with a fistfight and “possibly involved two motorcycle clubs.” Law enforcement sources told NBC News the fight happened between the Mongols biker gang and another biker gang.

White said it appears as though there was more than one shooter. "More than likely there was an exchange" of gunfire, he said.

There were conflicting reports about the identity of the other motorcylce gang involved. White would not name the motorcycle organizations, citing the ongoing investigation.

The law enforcement source told NBC News that two people from each gang were in grave condition.

The expo had been scheduled to continue Sunday but most events were cancelled "out of the interest in safety," White said. The motorcycle expo continued after the incident, with heavy security, police said. White said

VIEW FROM THE SCENE: pic.twitter.com/1GeYr1plc6 — Denver Police Dept. (@DenverPolice) January 30, 2016

The Colorado Motorcycle Expo bills itself on its website as "one of the largest motorcycle events in the country." It is taking place this weekend at the National Western Stock Show complex.

Initially, Denver police tweeted that the incident was at the Denver Coliseum, which is near the National Western Stock Show.