After Atlanta spa shootings, Colorado supermarket attack rocks US

A gunman opened fire at a supermarket in Boulder, Colorado, on Monday, killing 10 people, including the first police officer to arrive on the scene, before the bloodied suspect was arrested in the second deadly US mass shooting in a week.

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Police gave few immediate details of the latest shooting and no known motive for the violence, which unfolded at about 3 p.m. at a King Soopers grocery store in Boulder, a north-central Colorado city at the eastern foot of the Rockies, about 28 miles (45 km) northwest of Denver.

Frantic shoppers and employees fled for cover through the supermarket as law enforcement officers swarmed the scene, located about 2 miles from the University of Colorado's flagship campus.

Live-streamed video earlier had showed a white middle-aged man -- shirtless and seemingly covered in blood -- detained by police and led from the supermarket.

Dozens of armored vehicles, ambulances and armed personnel including FBI agents and SWAT teams were deployed to the scene.

Later, shoppers who had been led safely out of the store sat wrapped in blankets, talking to emergency workers in the snow-covered parking area.

"Our hearts are broken over this senseless act of violence," said King Soopers spokeswoman Kelli McGannon, praising "first responders who so bravely responded to these acts of violence."

The shooting follows another mass shooting last week at Asian-owned spas in the southeastern state of Georgia that left eight dead.

Colorado has previously suffered two of the most infamous mass shootings in US history.

In 1999, two teenage boys shot and killed 12 classmates and a teacher at Columbine High School before dying by suicide. 

Then in 2012, a heavily armed man stormed a movie theater showing a Batman film in Aurora, Colorado, murdering 12. The gunman is now serving a life sentence without the possibility of parole.