At least three people were killed in a shooting inside a Walmart store on Wednesday in suburban Denver, where police said they had not yet taken anyone into custody.
Police in Thornton, Colorado, did not immediately release any information about the circumstances of the shooting or who was responsible for the gunfire.
Two men were killed in the shooting. A woman, who was injured in the shooting, was taken to a hospital where she later died, Thornton Police Department said on Twitter.
"Detectives currently reviewing security footage & witnesses being interviewed for assistance with suspect(s)," police said on Twitter.
No one had been taken into custody, police said.
About an hour after the initial alert, police said on Twitter that the threat of gunfire had ended at the store, which was surrounded by police and fire crews.
"At this time this is NOT an active shooter. Active crime scene. We will update as info becomes available," the police department said in that tweet. Confirmation of the two fatalities came about 20 minutes later.
Thornton is city of about 120,000 people roughly 10 miles (16 km) northeast of downtown Denver.
Local NBC television affiliate 9NEWS reported that a woman whose son was in the Walmart had told her that he had heard about 30 gunshots and was still inside.
A video posted on Twitter showed the Walmart, which is situated in a large complex of big-box stores and other retail outlets adjacent to U.S. Interstate 25, apparently empty except for police officers with guns drawn.