The flames engulfing the building in the 21800 block of Avalon Boulevard turned into a 3-alarm fire shortly after 5 p.m.
Officials said more than 100 firefighters were on scene.
No one was seriously hurt.
The fire, which spiked 100 feet into the air, was fueled by the standing wood frame.
"All of the fire protection in modern construction is not in a place that is just frame," said Capt. Mark Savage of the Los Angeles County Fire Department.
That radiated heat combined with wind gusts sent the fire into a nearby mobile home park. More than 139 mobile homes were evacuated. At least 10 homes in the park were damaged by flames.
About 120 seniors living next door to the blaze were also evacuated.
"From what we've heard everybody is OK," said Jordan Pynes, the property manager. "They are seniors, but they are together so everyone is fine."
The planned 150-unit luxury apartment building was set to open July 2012.
The cause of the fire was under investigations. See photos of firefighters battling the blaze in Carson.