People watch an ambulance leave at the scene of a shooting at a Walmart in Thornton. -AFP

WASHINGTON: A man suspected of walking into a Walmart store in Colorado and "nonchalantly" shooting to death two men and a woman has been arrested, police said Thursday.

The seemingly random shooting Wednesday in Thornton, Colorado comes a month after a gunman killed 58 people in Las Vegas, the deadliest mass shooting in recent US history.

Police identified the suspect in the latest shooting as 47-year-old Scott Ostrem, and said on Twitter he had been taken into custody.

Police spokesman Victor Avila said the suspect calmly walked into the Walmart store at 6:10 pm.

Walmart employees and shoppers leave the scene of a shooting at a Walmart in Thornton. -AFP

"He walked in very nonchalantly with his hands in the pockets, raised a weapon and began shooting. Then he turns around and walks out of the store," the Denver Post quoted Avila as saying. "From what we have right now it appears to be random. It´s a crazy world we live in."

Police said the fatalities were two men and a woman. The female victim died later at the hospital.

More than 33,000 gun-related deaths occur annually in the United States, according to a study released this month.

Moves to curb gun ownership have failed repeatedly to make it through the US Congress over the years, despite a lengthening string of violent episodes.