The blaze erupted near Clementine and Santa Ana streets at about 7 p.m. When firefighters arrived, they encountered heavy smoke coming from the 3-alarm fire.
Crews were able to knock down the fire in two hours, according to Anaheim Police Sgt. Shane Carringer.
Video shows firefighters rescuing a family dog that was trapped in a second-floor unit. They were able to carry the dog down a ladder and it is expected to be fine.
One firefighter was treated for heat exhaustion and was expected to be OK.
No residents were reported injured, but the fire displaced them all.
The cause of the fire was unknown.