Several people have been killed in a supermarket shooting in the US state of Colorado after a gunman opened fire.
Officers arrived at King Soopers grocery store in Boulder before 3pm (local time) on Monday just minutes after a 911 call, the Boulder Police Department tweeted.
"We have multiple victims who lost their lives. One of the victims is a Boulder police officer," the department said.
Boulder Police Chief Maris Herold confirmed there were at least 10 fatalities.
"[The] hearts of this community go out to the victims of this horrific incident," she said.
Chief Herold identified the police officer who was killed as Eric Talley who was one of the first people at the scene, describing his actions as "heroic".
He had been part of the department since 2010.
"Officer Talley responded... he was the first at the scene, and he was fatally shot," Chief Herold said.
She said the weapon of the gunman was reported to be a "patrol rifle".
The police chief described the investigation as "complex" and it would take "no less than five days to complete".
"I am grateful for the police officers that responded and I am so sorry about the loss of Officer Talley and again we will be here working night and day," she said.
"We have one suspect in custody. I want to reassure the community that they are safe.
"We will try to do our best over the next few hours to identify the victims."
Tragedy struck as 'people were going about their day'
Boulder District Attorney Michael Dougherty said on Sunday night Boulder had suffered a "terrible and horrific mass shooting today".
He said Officer Talley's life was "cut far too short".
"I also want to stress how incredibly sorry I am for all the victims who were killed in King Soopers," Mr Dougherty said.
"These were people who were going about their day, doing their food shopping and their lives were cut abruptly and tragically short by the shooter who is now in custody.
"I promise the victims... that we will secure justice and do everything we must do to get justice in this case."
The shooting comes barely a week after a separate mass tragedy where a gunman opened fire at three massage parlours in the Atlanta area, killing eight people.
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