Multiple people killed in Colorado supermarket shooting

Police work on the scene outside of a King Soopers grocery store where a shooting took place (Joe Mahoney/AP)

A police officer is among “multiple” people who have died after a shooting at a Colorado supermarket.

Boulder police commander Kerry Yamaguchi said a suspect has been detained after the incident at the King Soopers store in Boulder on Monday.

Officers were seen escorting a shirtless man with blood running down his leg out of the store in handcuffs but authorities would not say if that was the suspect.

Boulder County District Attorney Michael Dougherty said authorities know how many people were killed and suggested they are not releasing the number because they need to notify families of the victims.

Police work on the scene outside a King Soopers grocery store where a shooting took place (David Zalubowski/AP)

He said: “This is a tragedy and a nightmare for Boulder County, and in response, we have cooperation and assistance from local, state and federal authorities.

Mr Yamaguchi said police were still investigating and did not have details on a motive for the shooting at the store in Boulder, which is about 25 miles northwest of Denver and home to the University of Colorado.

Dean Schiller told The Associated Press that he had just left the supermarket when he heard gunshots and saw three people lying face down, two in the car park and one near the doorway.

He said he “couldn’t tell if they were breathing”.

Video posted on YouTube showed one person on the floor inside the store and two more outside on the ground. What sounds like two gunshots are also heard at the beginning of the video.

My heart is breaking as we watch this unspeakable event unfold in our Boulder community. We are making every public safety resource available to assist the Boulder County Sheriff's Department as they work to secure the store.

Full statement: pic.twitter.com/m8nI24pahU

— Governor Jared Polis (@GovofCO) March 22, 2021

Law enforcement vehicles and officers massed outside the store, including Swat teams, and at least three helicopters landed on the roof.

At one point, authorities said over a loudspeaker that the building was surrounded and that “you need to surrender”.

Colorado Governor Jared Polis tweeted a statement that his “heart is breaking as we watch this unspeakable event unfold in our Boulder community”.