An early-morning fire in an Alameda apartment building displaced 20 people Wednesday after flames broke out in a first-floor unit, according to the Alameda Fire Department. Firefighters were called to the building on Central Avenue at about 4:30 a.m. and found people trapped on the third floor. Crews rescued three people, while another person jumped from the building and was taken to a hospital. The person’s condition was not immediately known. At least nine units were affected by the fire. Officials had not determined its cause.