BOULDER, Colo. (NewsNation Now) — Witnesses describe a chaotic scene as customers ran for the exits and first responders rushed to the area as shots rang out at a Colorado supermarket Monday afternoon.

Quinlyn Sloan told NewsNation that she was in the back of the store when the shooting began. She estimated she heard approximately 15 shots.

Brian Krusei says he had just checked out at the King Soopers supermarket and left out the front door when he heard what he thought were fireworks.

“I heard what I thought were fireworks and looked up kind of surprised that someone would be lighting off fireworks like that and I saw a guy wearing tactical gear running across the parking lot with an AR-15 style weapon, shooting,” Krusei told KDVR.

Krusei said he ran inside and told everyone about to leave because there was an active shooter outside. While he said people were taken aback at first, after they heard the shots they ran to an exit at the back of the store.

One witness who identified himself as Jim told a KDVR reporter on the scene that he was in the back of the supermarket when he began to hear the gunshots.

“Within a second or two there was just a cadence of pop, pop, it was more of like a full sound that I had never heard before and it was obvious it was a very dangerous situation,” he said.

Krusei said he also exited through the back before sheltering inside a nearby business.

“I was near the front of a stampede which just headed out… we just went flyin’ through those doors, we all just rushed and jumped about five feet down from the loading dock and just ran for our lives,” he said.

Citizen journalist Dean Schiller says he lives across the street from the grocery store and was inside when shots rang out.

“We heard gunshots go off, it sounded like a heavy caliber type, maybe a shotgun,” Schiller said. “I never saw anyone but I saw some victims as I came around the corner.”

Schiller said he saw three victims lying still on the ground and initially heard “at least” a dozen shots.

Schiller says he immediately began streaming live on YouTube and eventually thousands watched his perspective as police and SWAT teams arrived on the scene.

“I have some friends who were in there who are very close to me, I’m just hoping they’re alright,” he said.

Mason Chronowski works at a tattoo shop nearby the grocery store.

“We were all working, tattooing like it was a normal day, then we heard a couple of what sounded like gunshots — so we went outside to kind of investigate what was going on, and then a bunch of police units showed up,” Chronowski said. “We’re all a little shook up.”

Chronowski said they were told to remain inside the shop as wave after wave of police officers arrived on the scene.

“It could have very well easily been any of us, so I’m just grateful for my health and everybody else’s health around here and I hope everyone else is ok,” Chronowski said.