The building was reportedly fully engulfed in flames when firefighters arrived, and the fire quickly spread to nearby buildings.
Firefighters evacuated several nearby buildings, including a senior center, and one woman was treated for smoke inhalation.
Flames could be seen all over the city of Alhambra.
The fire burned down the building that was reportedly supposed to be a complex for senior citizens and damaged some neighboring apartments. The Red Cross is helping displace residents.
Battalion Chief Ray Mosak from the Alhambra Fire Department said the cause of the fire has not been determined.
Firefighters continued to douse the building with water early Wednesday morning.
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