A gunman has killed at least 10 people, including a police officer, following an hours-long stand-off in a grocery market in Colorado, police officials told United States media.
One person of interest has been taken into custody, but no motive has been released. That person was injured in the incident, said Kerry Yamaguchi, a commander with the Boulder police department.
Police have yet to give details about the casualties or the suspected gunman.
The shooting began around 14:30 local time when someone entered the grocery store and began firing.
The Boulder police tweeted some 20 minutes later that there was an "Active Shooter at the King Soopers on Table Mesa" street.
Two hours later, the police warned people again to avoid the area. "Do NOT broadcast on social media any tactical information you might see," the tweet added.
However, some of the stand-off was captured on camera by a passer-by showing victims near the grocery store.
US President Joe Biden has been briefed about the shooting, the White House said.
On Twitter, Colorado Governor Jared Polis said: "My prayers are with our fellow Coloradans in this time of sadness and grief as we learn more about the extent of the tragedy."