The violence occurred at Denver Coliseum where the motorcycle expo was taking place on the sidelines of a livestock show on Saturday.
A witness quoted by the Denver Post said the feud was started by rival bikie gangs.
No arrests have been made, a Denver police spokeswoman said.
The spokeswoman told reporters there were shots fired and at least one stabbing.
"We do have one deceased party and multiple other victims," the spokeswoman said.
The motorcycle expo was shut down, and police escorted people out of the building, the Post said.
The National Western Stock Show continued its programme.
