At least 12 people were killed, including a sheriff’s sergeant, late Wednesday night when a gunman clad in black opened fire during a “college country night” at a bar in Thousand Oaks, California, police said.

Hundreds of people were inside the Borderline Bar & Grill. Shots rang out at around 11:20 p.m., Ventura County police said, when the shooting started.

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Deputies and highway patrolmen arrived on the scene within minutes of getting multiple calls of shots fired, Sheriff Geoff Dean said in a late night press conference.

Sheriff’s Sgt. Ron Helus, a veteran of 29 years, and a patrolman entered the bar after hearing more gunshots. When they went through the front door, Helus was struck multiple times by gunfire.

The patrolmen rescued the deputy from the line of gunfire and he was taken to a local hospital, where he died early Thursday.

Related: The Hero in the California Shooting Was a Dedicated Cop

“It is a horrific scene in there. There is blood everywhere,” Dean said.

Witnesses inside the club told local news outlets that patrons used chairs to break windows and hid in the club’s attic in between rounds of gunfire.

Several witnesses told TV stations that a tall man clad all in black with a hood and his face partly covered first shot at a bouncer working the door, then opened fire, seemingly at random, at the people inside.

“I knew it was live, knew it was real,” a 56-year-old witness told KABC-TV.

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“He [the gunman] didn’t say anything at all. He just started shooting.”

A woman who was at the bar at the time of the shooting said the gunman “knew what he was doing.”

“While I was inside I would say [I heard] … about a good 30 seconds [of gunshots] … He had two rounds that I know with him. He changed them within about six seconds, which was really fast,” she recalled.

“So he knew what he was doing and he also had perfect form. When I looked back he was spot-on,” she added.

Police told The Los Angeles Times that at least 30 shots were fired and the gunman used smoke bombs. It was unclear what type of weapon the shooter used.

Witnesses said many inside were college students from Pepperdine University, California State University Channel Islands and California Lutheran University.

Some survivors of the Las Vegas mass shooting were also inside the bar.

Chandler Gunn, 23, of Newberry Park, called a friend who works at the Borderline Bar & Grill, who was also at Route 91 in Las Vegas, The Los Angeles Times reported.

“A lot of people in the Route 91 situation go here,” he said, referring to the mass shooting last year in Las Vegas.

“There’s people that live a whole lifetime without seeing this, and then there’s people that have seen it twice.”

Josh Coaly, 27, had been to Borderline several times with his friends, including one who also survived the Vegas shooting, The Times reported.

Coaly told the paper that his friend said he is with his dad and is in good condition.

Carl Edgar, 24, of Tarzana, told The Times he had about 20 friends inside the bar, which he frequently attends.

“As far as I know, all of my friends are OK, safe,” he said. “There are a few people we can’t get a hold of, but in these situations, people usually turn off their phones to be safe so I’m not gonna get too worried. A lot of my friends survived Route 91. If they survived that, they’ll survive this.”

Police said the shooter was dead inside the bar. It was unclear how he died.

About a dozen heavily armed officers were seen lining up against a wall, appearing to prepare to storm the building. Medical workers were seen loading at least one victim onto a gurney, preparing him for transport.

About a dozen heavily armed officers were seen lining up against a wall, appearing to prepare to storm the building.

Medical workers were seen loading at least one victim onto a gurney, preparing him for transport.

Additional units from the California Highway Patrol, Simi Valley and the F.B.I. responded, he said.

About a dozen heavily armed officers were seen lining up against a wall, appearing to prepare to storm the building. Medical workers were seen loading at least one victim onto a gurney, preparing him for transport.

Aerial footage showed armed officers entering the nightclub and numerous police vehicles outside.

Police vehicles and fire engines were seen blocking off traffic in the surrounding area.

Other officers appeared to be scattered in the vicinity.

Thousand Oaks is about 40 miles up the coast from Los Angeles.

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This is a developing story. Please check back for updates. Fox News’ Amy Lieu and The Associated Press contributed to this Fox News report, which is used by permission.

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