An officer at the LAPD's Van Nuys Station said police responded to a burglar alarm about 3:30 a.m.
"When the officers arrived, they found the door pried open, they could hear noises on the inside," police Lt. John Romero told KTLA5.
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A man who lives in the house where the suspect may have entered but who was not at home this morning told police he has an extensive collection of firearms, according to broadcast reports from the scene.
After additional officers arrived to secure the location, motion detectors inside the home in the 14900 block of Gilmore Street were activated, an additional panic alarm went off and sounds were heard from inside, Romero said.
"We believe that the suspect is still contained in the house," Romero told KTLA shortly after 8 a.m.
The burglar alarm brought dozens of SWAT and K-9 officers to the area of Victory Boulevard and Kester Avenue and prompted police to close off the intersection and surrounding streets to traffic.
Residents from about a dozen homes and two multi-story apartment buildings were evacuated, Romero said, adding that the gymnasium at nearby Van Nuys High School, which is closed for the holidays, has been opened for evacuees.