Investigators said the gunman walked up to a crowd standing in a courtyard in the complex and started shooting. The suspect ran off on foot after the incident.
Three men and two women were taken to the hospital. Officers said two people suffered serious injuries.
The suspect is described as a Hispanic man in his early 20s. A motive for the shooting was not immediately known. Anyone with information on the crime is asked to call Pomona police detectives at (909) 620-2095.