ORANGE (CBSLA.com) — The cause of a fire that killed one person and injured another at an Orange County apartment complex was under investigation Friday.

The second-alarm fire was reported around 11:15 p.m. Thursday at the Santiago Apartments in the 200 block of W. Lincoln Avenue in Orange, officials said.

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The first crews on scene reported heavy smoke and fire coming from the complex.

“The fire conditions were rapidly expanding and due to the size of the complex, it took a lot of personnel to get hose lines stretched back deep within the complex,” Capt. Casey Fieldhouse said.

An elderly woman found outside the burning building suffered critical burn injuries and was transported to a local hospital.

The body of an unidentified elderly man “was found during a search of an involved unit, and declared dead on scene,” Orange fire officials said.

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A total of six units were involved in the fire, with two suffering heavy damage.

It took 50 firefighters from several departments about 30 minutes to knock down the fire.

One firefighter suffered a minor injury and was treated on scene.

Several residents have been displaced and were being assisted by the Red Cross.

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A damage estimate was not available.