Someone has shot and killed as many as 30 buffalo on a private ranch and the Park County Sheriff's Office is trying to figure out who.

Park County Sheriff Fred Wegener was notified about the slain buffaloes on Wednesday, at about noon. The tipster said a shooter was actively gunning down the bison in the area near Eleven Mile Reservoir.

“We’re certainly concerned about what went on out there,” Wegener told 7NEWS.

“We believe we have contacted all of the individuals involved in the actual hunting,” Wegener said the sheriff's office had interviewed 12 people Thursday afternoon.

Wegener said the bison were illegally hunted on several hundred acres of federal and state land.

The exact number of slain buffalo has not been determined but could be us many as 30, and a motive is not known, according to Wegener.

The investigation into the mass shooting is in the preliminary stage and is ongoing at this time, the sheriff's office said.

“No one has been charged,” Wegener said and explained potential charges could include trespassing and cruelty to animals. No suspects have been identified.

The investigation is being conducted by the Park County Sheriff's Office, the District Attorney's Office and the Colorado State brand inspector assigned to the area.

Park County has had privately owned buffalo herds for many years, Wegener said.