Hunt for gunman after US Walmart shooting

Denver police are hunting a man who "nonchalantly" walked into a Denver Walmart store and fired a handgun at shoppers, leaving two men and a woman dead.

Thornton police reported "multiple parties down" on Wednesday night and advised people to stay away from the area as dozens of police cruisers and emergency vehicles raced to the scene.

The men died at the store and the woman died in hospital.

No one has been arrested.

Police spokesman Victor Avila said the man fled in a car after opening fire at the hypermarket.

"This is a very heinous act," he said.

"We don't know exactly what the motive of the person was but it was certainly a terrible act."

He there was no indication the shooting was an act of terrorism.

Investigators, who have not released any other details about the circumstances of the shooting, were reviewing security footage and interviewing witnesses.

Special agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives were helping police in the investigation.

The Walmart, about 16km north of downtown Denver, is in a busy shopping centre that includes restaurants, a cinema and several other stores.