Colorado shooting: Three killed at Walmart in Thornton as customers flee in panic

Two men and a woman were killed in a shooting inside a suburban Denver Walmart on Wednesday night that forced customers to either hide or flee.

Thornton police reported "multiple parties down" 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 Colorado store, and the woman died at a hospital.

Police spokesman Victor Avila said a man nonchalantly entered the store and fired a handgun into a group of people before fleeing in a car. No one has been arrested.

"This is a very heinous act," Avila said. "We don't know exactly what the motive of the person was, but it was certainly a terrible act."

The spokesman said there is currently no indication that the shooting was an act of terror.

Denver Walmart shooting map

Reports of shots fired came shortly before 6:30 p.m. local time, a police spokesman told local 9NEWS in Denver.

An hour after the incident, the situation, the nature of the incident or status of the threat remained unclear, he said.

Local television images showed a number of police cars and ambulances surrounding the store, lights flashing. 

Aaron Stephens, 44, was in the self-checkout line when he heard a single shot followed by more bursts of gunfire, The Denver Post reported. He said customers started screaming and running for the exits.

"I was scared. I feared for my life," said Stephens, who has lived in Thornton for 20 years.

Meanwhile, Brandon Bonney said he received a call from his brother, who was inside the store.

"Bro, I'm inside Walmart, and there's a shooting here," Bonney said his brother told him.

Bonney told his brother to silence his phone, stay calm and "just get somewhere and hide," The Post reported.

Investigators have not released any details about the circumstances of the shooting or the condition of the injured woman.

Local NBC affiliate 9NEWS reported that a woman whose son was in Walmart had told her that he had heard about 30 gunshots and was still inside.

A video posted on Twitter showed the store apparently empty except for police officers with guns drawn.

One woman on Facebook said her son had told her there was a shooting at the store.

"OMG! My son Nathan just called me shooting at Thornton Walmart just now..many shots fired!!" Junie Toni Manz wrote on Facebook.

"Angela Martinez-Garcia and her son Johnny and her mom Meka were in the store during shooting and had to run out...They are shaken up."