At least 12 people have died, and 10 more are injured after a mass shooting at a country bar called Borderline Bar & Grill in Thousand Oaks, Calif., late Wednesday night (Nov. 7).

ABC News reports that a white male gunman burst into the bar where hundreds of people were gathered, throwing smoke grenades to cause confusion and firing dozens of rounds into the crowd. Authorities responded to Borderline just before midnight, including California Highway Patrol, a SWAT team and FBI.

Sgt. Ron Helus was one of the first officers on the scene, and he was struck multiple times as he entered the bar through the front door. Helus — a 29-year veteran of law enforcement who was scheduled to retire soon — was among the fatalities. The gunman, who has not been identified, also died in the shooting, though the circumstances of his death remain unclear.

Speaking to Good Morning America, Teylor Whittler, who was at Borderline celebrating a friend's birthday, described the scene as the shooting took place.

"A bunch of people dog-piled on top of each other," she says." "Everyone just yelled, 'Run, he's coming!'" She says she stumbled and fell, and multiple other people stumbled over her before a man helped her to her feet. Whittler says multiple other men gathered around a group of people who were trying to escape, "ready to take a bullet for every single one of us."

Twenty-one-year-old Taylor von Molt, a promoter at Borderline, tells CNN that when the shooting began, people were line dancing, and she thought the initial gunshot she heard was a balloon popping.

"I was confused because we didn’t have any balloons at the time... I turned around and saw him fire his weapon a couple of times and I ran to the nearest exit and tripped and fell on the way.," she recalls.

Ventura County Sheriff Geoff Dean described the scene inside the bar after the mass shooting in Thousand Oaks as "horrific," with "blood everywhere." The motive for the shooting was unclear as of Thursday morning (Nov. 8). Dean says investigators have so far not found an assault rifle inside the bar.

"Right now as far as we know there was only one handgun, but that could certainly change as we do a more thorough search of the building," he says.

Borderline Bar & Grill's website describes the venue as "Ventura County's Largest Country Dance Hall & Live Music Venue," listing John Rich, Collin Raye, Mark Chesnutt, Lee Brice and Tyler Farr among the artists who have performed there over the years.

This is a developing story. Taste of Country will update developments in the mass shooting in Thousand Oaks, Calif., as they happen. 

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