Three people were injured Friday in a fire at a 12-story residential building in downtown San Diego. The fire broke out around 10:30 a.m. on Sixth Avenue near A Street, according to the San Diego Fire-Rescue Department. Firefighters extinguished the blaze on the sixth floor and then worked to clear smoke from the building, officials said. Fire officials reported that three people were injured, with two of them taken to UC San Diego Medical Center in Hillcrest. The extent of the injuries was not immediately known. A total of 44 personnel were assigned to the fire, including six engines, three medics and two trucks, officials said. The cause of the fire was under investigation.