US police say “multiple people” have been killed in a shooting at a supermarket in Boulder, Colorado, including a police officer.

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

A witness told the Associated Press he heard gunshots and saw three people lying face down on the ground, adding that 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, but the extent of their injuries was not clear.

SWAT teams and at least three helicopters were sent to the scene.

Boulder Police did not given further details about the shooting or how many people were killed. They said police were still investigating and didn’t have details on a motive.

Boulder County district attorney Michael Dougherty said authorities know how many people died but suggested they are not releasing more information at this stage because families of the victims have yet to be notified.

The FBI said it is helping with the investigation.

Earlier, Colorado governor Jared Polis tweeted to say he was heartbroken.

He said: “My heart is breaking as we watch this unspeakable event unfold in our Boulder community.”

He called it “very much an active situation” and said the state was “making every public safety resource available to assist the Boulder County Sheriff’s Department as they work to secure the store.”

White House press secretary Jen Psaki tweeted that President Joe Biden had been briefed on the shooting.

In a statement, the King Soopers chain offered “thoughts, prayers and support” to those effected.

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