At least 13 people were killed in a mass shooting at a bar in Southern California overnight after a gunman forced his way into the building, according to authorities.

The gunman, who is believed to be among the dead, burst into the bar around 11:20 p.m., cloaked in all black as he threw smoke bombs and began shooting at targets as young as 18 authorities and witnesses said. Several witnesses described the weapon used as a pistol. (LA Times)

"We have no idea if there is a terrorism link or not," Ventura County Sheriff Geoff Dean told reporters.

The shooting took place at the Borderline Bar and Grill in Thousand Oaks, California.

Ventura County Sheriff’s Department Sgt. Ron Helus engaged the suspect along with a California Highway Patrol officer. According to the LA Times, Helus was shot multiple times and died at a local hospital.

The gunman is also dead.

The bar was holding a college country nights event between 9 p.m. and 2 a.m. on Wednesday night, its website states.

Hundreds of people -- including students from California Lutheran University, private Christian school Pepperdine University and California State University Channel Islands -- were inside Borderline Bar & Grill in Thousand Oaks, Calif., for the country music event when shots suddenly rang out at about 11:20 p.m., Ventura County police said. Deputies and highway patrolmen arrived at the bar within minutes of receiving multiple 911 calls and began assessing the grim, gruesome situation, Sheriff Geoff Dean said during an early Thursday press conference. (Fox News)

One witness, Taylor Whitler, told media the gunman “knew what he was doing.”

“I heard the gunshot, I turned around, and I saw him shoot a couple more times,” the 19-year-old said. “In a split second everyone yelled ‘get down.’ I ran to the left of the dance floor where the back door is and everyone pretty much piled on top of each other.”

She continued: “He had two rounds that I know with him. He changed them within about six seconds which is really fast, so he knew what he was doing. He also had perfect form, when I look back he was spot on.”

Update: Ventura County Sheriff Geoff Dean has identified the suspect as Ian David Long, a 28-year-old Marine Corps veteran. The suspect was known to law enforcement. Dean says he doesn't think the shooting was random, because the suspect lived in the area.

Update:

President Trump has weighed in, tweeting that he's been briefed on the mass shooting.

I have been fully briefed on the terrible shooting in California. Law Enforcement and First Responders, together with the FBI, are on scene. 13 people, at this time, have been reported dead. Likewise, the shooter is dead, along with the first police officer to enter the bar.... — Donald J. Trump (@realDonaldTrump) November 8, 2018

....Great bravery shown by police. California Highway Patrol was on scene within 3 minutes, with first officer to enter shot numerous times. That Sheriff’s Sergeant died in the hospital. God bless all of the victims and families of the victims. Thank you to Law Enforcement. — Donald J. Trump (@realDonaldTrump) November 8, 2018

This story will be updated with additional information.