At least 14 people were killed and a suspect was dead Wednesday after up to three gunmen on a “mission” barged into a holiday party in a California conference room and unleashed a bloodbath, law enforcement sources told NBC News.

The gunman or gunmen fled in a black SUV after the shooting about at 11 a.m. (2 p.m. ET), police said.

About 4½ hours later, multiple police cars were involved in a high-speed chase nearby with three people in a dark truck or SUV, law enforcement sources told NBC News. Two of the suspects were shot, the sources said — one was killed, and the other was unresponsive after having been wounded in the chest.

The third suspect remained at large, law enforcement sources said.

San Bernardino police Sgt. Vicki Cervantes the location of the third person wasn’t immediately clear, but she said a third subject was believed to be “outstanding.”

Photos: Deadly Mass Shooting in San Bernardino, California

In addition to the 14 dead:

  • The shooting erupted during a holiday party in a conference room.
  • At least 10 of 17 wounded are in critical condition.
  • Police shot two suspects after a high-speed chase in a shootout hours later.
  • One of the suspects was killed.
  • A police officer was wounded in the shootout.

Cervantes said that one officer was shot in the confrontation but didn’t suffer a life-threatening wound and that one suspect possibly remained at large.

Seventeen other people were wounded when the shooting started inside the Inland Regional Center in San Bernardino, about 55 miles east of downtown Los Angeles, police said.

Authorities said 10 of the 17 injured were taken to hospitals in critical condition. Fire Chief Tom Hannemann said three people were in serious condition.

It appeared to be the worst mass shooting since the December 2012 slaughter of 20 first-graders and six staffers at Sandy Hook Elementary School in Newtown, Connecticut.

“These people came prepared to do what they did as if they were on a mission,” San Bernardino Police Chief Jarrod Burguan said. “They were armed with long guns, not with handguns.”

Burguan added, “The suspects have fled.”

Gallery: Deadly Mass Shooting in San Bernardino, California

“We don’t yet have a motive,” the chief said, adding that the getaway vehicle was a black SUV of some kind.

Burguan warned that the death toll could climb as investigators continued to search the building. “This is a tragedy,” he said.

David Bowdich, the FBI’s assistant director in Los Angeles, stressed that “we don’t know if this is a terrorist incident.”

Neither Burguan nor Bowdich would confirm reports that at least one of the suspects was believed to be wearing tactical gear.

California Gov. Jerry Brown canceled the state’s annual Christmas tree lighting ceremony Wednesday night “out of respect for Californians affected by today’s tragedy,” although the tree itself will still be lighted.

“California will spare no effort in bringing these killers to justice,” Brown said.

Related: What Is Inland Regional Center?

Luis Gutierrez said that he spoke to his wife, who works in the facility, and that she told him that a gunman she saw was dressed all in the black, wearing a flak jacket of some kind and a mask on his face. He said the people on her floor began barricading their doors after hearing the shots.

While law enforcement briefed reporters inside the state facility, firefighters set up a triage area outside the complex on South Waterman Avenue, where they were treating the wounded on the street and loading others into waiting ambulances for treatment at nearby Loma Linda Medical Center.

Some were transported in the backs of pickup trucks.

Meanwhile, all San Bernardino city buildings, the courthouse and all the San Bernardino County buildings were placed on lockdown.

President Barack Obama was briefed by Lisa Monaco, his homeland security adviser, and asked to be updated as the situation develops, a White House official said.

Related: Obama Calls for Gun Law Changes After Latest Mass Shooting in California

“Absolutely heartbreaking,” Sen. Dianne Feinstein, D-California, tweeted.

Marybeth Feild, president of the center’s board of trustees, said the gunfire erupted in a conference room where the San Bernardino County Department of Public Health was holding a banquet.

Outside, the normally tranquil suburban streets were jammed with police vehicles and first responders.

Dozens of SWAT team officers massed outside the facility, while police evacuated the occupants who filed out with their hands up.

Police also cleared out nearby buildings and marched the occupants out of harm’s way to a nearby golf course.

In addition to the FBI, agents of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were on the scene, officials said. So was the police bomb squad.

“There were some things that were in the building that were not immediately identifiable that caused us concerns,” Burguan said.

A man who identified himself only as Jim, a sales person at the nearby Structural Material Company, told NBC News that the neighborhood was an armed camp.

“There’s plenty of police activity,” Jim said. “A lady ran into our bathroom and said somebody was shooting there.”

Authorities respondto a mass shooting in San Bernardino, California, where there were as many as 20 victims. NBC Los Angeles

Jim said police told him and the staff — about 10 to 12 people — to stay inside the building, which is about 200 to 300 yards from the Regional Center, a state-run center for people with developmental disabilities.

The mayhem came just days after a gunman barged into a Planned Parenthood facility in Colorado Springs, Colorado, killing three people during a five hour siege.

Democrat Hillary Clinton was the first of the presidential candidates to weigh in on the unfolding tragedy.

“I refuse to accept this as normal,” she tweeted. “We must take action to stop gun violence now.”

She was followed by Democratic rivals Martin O’Malley and Bernie Sanders and Republican candidates Donald Trump. Ben Carson, Ted Cruz, Jeb Bush, John Kasich, George Pataki, Lindsey Graham, Chris Christie and Mike Huckabee.

“California shooting looks very bad,” Trump tweeted. “Good luck to law enforcement and God bless. This is when our police are so appreciated!”

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