The fire started in the upper unit of the two-story structure at 1823 Foothill Blvd. at 10:18 p.m. and was controlled by 36 firefighters at 10:44 p.m., Battalion Chief Melinda Drayton said.
The cause of the blaze has not yet been determined, Drayton said. Six people who lived in the lower unit were able to get out on their own, according to Drayton.
She said they declined an offer of assistance from the American Red Cross and chose to stay with friends and family until the unit is repaired.
The lower unit only sustained water damage and it's expected that the residents will be able to return soon, Drayton said.
A family was preparing to move into the upper unit and had moved some furnishings inside, but no one was present during the fire, she said.
The upper unit sustained more damage than the lower unit and the family that was preparing to move in might have to wait for a while, Drayton said.
The only injury from the fire was to a man who was treated for smoke inhalation, Drayton said.
It's not immediately clear whether he was a resident or just happened to be in the area, she said.