The fire was reported at 4:18 a.m. at a two-story, four-unit apartment building at 1607 Santa Clara Ave., Alameda fire Capt. James Colburn said.
No occupants were injured, but one firefighter sustained non-life threatening injuries, according to Colburn.
The firefighter was taken to a local hospital for treatment.
The blaze was knocked down by 4:42 a.m., and the cause and origin of the fire remain under investigation.