At least one person has been killed and multiple others injured after what one bystander described as a fight between rival biker gangs at a motorcycle exposition in Denver, police told the Denver Post.

At least two people had been shot and one stabbed during the incident at the National Western Complex, where the Colorado Motorcycle Expo was being held, police spokesman Sonny Jackson said. Initial reports cited the Denver Coliseum, which is in the proximity of the complex, as the site of the incident.

The bystander asked the Denver Post for anonymity out of fear of retaliation.

At least nine people have been sent to area hospitals, according to Denver Health.

Of the seven sent to Rocky Mountain Regional Trauma Center, one has died, three are in critical condition and three in stable condition, Denver Paramedics medical director Kevin McVaney said.

McVaney said the hospital was on lockdown. Officials would not elaborate on the purpose of the lockdown.

Police Technician Raquel Lopez said she couldn't provide an exact number of the injuries. She also couldn't say whether any gangs were involved.

No arrests have been made.

Bob Cook told the Denver Post (http://dpo.st/1SsnPvS ) that the shooting happened near his leather goods company booth.

Cook said he heard two shots fired and saw people dive under tables. He said he didn't hear any arguments before the shooting and doesn't know what prompted it.

A posting on the Colorado Motorcycle Expo Facebook page said the event was going on as scheduled Sunday.

"Rest assured that all of the offending parties have been ejected and all is well," the posting said.

No information was immediately available on the identities of those injured.

Fox News' Will Carr and the Associated Press contributed to this report.