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TUSTIN (CBSLA) — Firefighters battled a five-alarm blaze at an apartment building in Tustin early Wednesday.

Flames were first reported at about 3 a.m. at the Chatham Village Apartments, 15751 Williams Street. Firefighters arrived to find the building fully engulfed.

Within 25 minutes of starting the firefight, the roof collapsed, and all firefighters were pulled out of the building, Orange County Fire Authority Capt. Tony Bommarito said. Video shows a portion of the smoldering roof falling off the building and falling onto the sidewalk, forcing firefighters back.

About 125 firefighters battled the blaze from a defensive position outside the two-story, 100-unit complex. At least 40 units have been damaged by smoke.

Some residents who escaped the two-story building say they were awoken to the sound of people screaming and pounding on doors, but fire officials say they have not confirmed all residents got out. Residents displaced by the fire were asked to check in with the Red Cross at 1952 E. McFadden Ave. in Santa Ana.

Two residents were taken to a hospital for smoke inhalation.