A woman who lives at the two-story building, located at 1445 Kerley Drive, reported at 6:01 a.m. that smoke was coming from one of the building's first-floor apartments, fire Capt. Mary Gutierrez said.
The woman had knocked on the door of that apartment and no one answered, Gutierrez said.
Firefighters arrived at the building at 6:06 a.m. to find thick smoke coming from the apartment.
There was an initial report that someone needed to be rescued, but fire crews evacuated the building and all of the more than 20 residents were accounted for, Gutierrez said.
Firefighters knocked down the blaze in about 20 minutes.
The apartment where the fire started sustained significant smoke damage, and the man who lived in the unit was displaced, Gutierrez said.
She credited the woman who reported the smoke with helping to prevent further damage.
"It was detected early because one of the residents smelled smoke and came out -- she did an incredible job of alerting the occupants," Gutierrez said.
No injuries were reported.
Investigators are working to determine the cause of the fire.