Multiple people were killed at a King Soopers grocery store in Boulder, Colo., on Monday, including a Boulder police officer, after a shooter opened fire on customers and responding officers.

A suspect is in custody, though police officials did not offer a potential motive. Officials did not report the number of fatalities, and said that the only seriously injured person was the shooter.

Dozens of emergency response vehicles lined the streets around the store Monday afternoon as police responded to what they described as an “active shooter.” Witnesses described a chaotic scene, with customers rushing to exits at the front and back of the store after shots were fired. One witness told local media that the shooter did not say anything before opening fire.

Video from a witness who was live-streaming on YouTube from the store’s parking lot showed at least two people injured and motionless on the ground outside and a third just inside the front doors.AD

A little after 5 p.m. local time, Boulder Police said it was responding to another report of an “armed, dangerous individual," and asked residents near the second location to “shelter in place." It was unclear if the police activity at the second location was related to the supermarket shooting.

“There are gunshots inside the store! People ran out of the back door! The active shooter is still in there!” the witness who was live streaming shouted.

The live video showed heavily armed officers surrounding the building — with its front windows broken in — and police could be heard trying to communicate with the attacker via bullhorn. At one point, officers were lifted onto the roof in a cherry picker.

Around 3:30 p.m. local time, a man in handcuffs who was bleeding down his leg was guided away from the building by police.

Several law enforcement jurisdictions were seen during the response, beyond the Boulder Police Department, including the Jefferson County Sheriff and the nearby Broomfield Police Department. Officers from the Federal Bureau of Investigation were also seen. Andrew McCabe, who served as the FBI’s deputy director from 2016 to 2018, told CNN representatives from the local FBI office were likely there to offer assistance and offer support, even if it’s not a federal crime scene.AD

As details of the attack emerged slowly Monday evening, government officials shared their sorrow and condolences.

“My heart is breaking as we watch this unspeakable event unfold in our Boulder community,” Governor of Colorado, Jared Polis, said in a written statement. “We are making every public safety resource available to assist the Boulder County Sheriff’s Department as they work to secure the store."

Polis had said earlier he was “closely watching unfolding events."

Rep. Joe Neguse (D-Colo.), sent his prayers to the Boulder community, first responders and law enforcement who responded to the “terrible incident,” he wrote on Twitter.

Meanwhile, those who experienced and survived the attack offered details of the horrific scene.

A witness who spoke to the Denver Post said the shooter did not say anything — “he just came in and started shooting.”AD

A man named Steven told 9News his grandchildren were inside the store during the shooting. He said they hid in the closet as the incident unfolded and as police dropped into the store through the roof.

Daniel Douglas was in the store picking up lunch and flowers for his girlfriend when the gunshots began.

“Nobody knew what was going on so we started screaming: ‘Hit the ground,’” he told Fox 31 Denver.

At some point, he said, the shooter moved to the front of the store, while Douglas and other customers rushed to the back of the building, where he said many others were hiding and trying to escape. A co-worker who was with him at the moment had to kick the emergency-exit door open so people could get out, he said.

“A lot of people were petrified. A lot of people were crying,” he said.

Another man, who said he was on his way to pick up coffee at the store, walked away from the incident unharmed. He told Fox 31 he was “terrified” and “in shock” when he first realized what has happening.AD

He said he called his mother to let her know he was all right, then “it all kind of sunk in and I started panicking,” he said.

“The fact that it’s happening all over America,” he added, “seeing it on the news, like, something I’ve grown up with, like people my age and my generation — we’re used to this, and its just never something that I think would happen in my town.”

Ryan Borowski, another survivor, expressed the same shock and disbelief about the shooting, which took place in the otherwise peaceful city of Boulder.

“Boulder feels like a bubble and that bubble burst,” said Ryan Borowski on CNN Monday night. “It feels like nowhere is safe." Borowski said he was inside King Soopers supermarket to get a bag of chips and a soda when the shooting started.

There have been as many as nine school shootings in the area since the Columbine massacre in 1999, which left 12 students and a teacher dead. Four other major shootings have occurred within 20 miles of the suburban Columbine High School high school, including a 2012 shooting at a movie theater in Aurora that left 12 dead.

This is a developing story and it will be updated.

Annie Gowen, Nicki DeMarco and Justin Scuiletti contributed to this report.