The first officer on the scene of a shooting that left 14 dead at a holiday party in California described a surreal and hellish scene of "unspeakable carnage" and "pure panic" amid Christmas trees and decorated tables.

San Bernardino police Lt. Mike Madden gave his up-close account at a news conference Thursday night.

A 24-year police veteran who grew up in the city, Madden usually works a relatively dull desk job that includes supervising the department's dispatchers, whose voices he knows well. That made the first call as he was driving to lunch especially alarming.

"I could hear it in our dispatcher's voice that this was actually happening," Madden said. "We have an active shooter, we have an active shooter going on in our city."

Madden was less than a mile away, and he and another officer arrived simultaneously, and "just out of pure luck" he pulled into best possible parking lot of the large social services center.

The husband-and-wife shooters, he would later learn, were already fleeing and would later die in a gunbattle with police, but, he said, "We had every belief at that time that we had people still actively being shot."

Within two minutes a team of four officers had gathered, and they went in.

They found horror and chaos.

The smell of gunpowder was in the air. Fire sprinklers were spraying. Fire alarms were blaring, along with much worse sounds, the "moans and wails" of the wounded.

"There were people who were obviously injured, and obviously in great amounts of pain," Madden said.

"It was unspeakable," he said, "the carnage that we were seeing, the number of people that were injured and unfortunately already dead, and the pure panic."

Madden said he had to make the very difficult decision to walk past the wounded and the dead to try to find the shooters.

The officers found some 50 people in a back hallway, frozen in fear, making Madden worry that the gunmen were among them and holding them hostage.

"They did not want to come to us," Madden said. "We had to tell them several times, 'Come to us!' 'Come to us!' Once the first person came forward it opened the floodgates."

He said the people poured past them and out of the building as a flood of other first-responders poured in and began helping the injured and clearing the building.

Madden then faded back into a more familiar supervisor role, but he remained shaken a day later, and didn't expect the feeling would go away anytime soon.

"This was tragedy that I've never experienced in my career, and I don't think most officers do," he said. "We resolved that situation quickly, but there's so much tragedy that's left behind."