LOS ANGELES (CBSLA) — Firefighters are mopping up a fire that broke out inside a vacant Exposition Park building where homeless people were believed to be sleeping early Monday.

Neighbors called 911 at about 2:30 a.m. to report the fire at a vacant building near South Flower and 38th Street. The building once housed a community services center.

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Firefighters arrived to see large flames shooting high into the air and initially rushed in, but had to back out because the roof was starting to collapse.

“They were huge flames,” resident Mike Davis said. “And in fact they were beginning to come off of the roof at the time. I began to hear crackling.”

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Residents in the area were concerned that people had been sleeping inside the building, but fire officials said they have not found anyone.

“When we arrived, my friend and I saw three homeless guys, two running toward Figueroa, one across the street. They didn’t have shoes,” witness Pedro Ortega said. “I mean, they were probably asleep inside, or something like that. That’s what we guess.”

Los Angeles Fire Department Asst. Chief Antoine McKnight said firefighters performed an initial search when they arrived, and again when the fire was knocked down.

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No injuries were reported. The fire is under investigation.