SAN FRANCISCO (KGO) -- Firefighters are searching for the cause of a fast-moving, three-alarm fire that started early Friday morning in San Francisco's Richmond District.The fire left four people hurt, including a firefighter, and more searching for a new place to live.The sound of the fire crackling could be heard over the sirens of almost 100 San Francisco firefighters rushing to the Outer Richmond neighborhood just before 2 a.m."When we got here on the scene, the fire was blowing through the roof of the structure," SFFD Batt. Chief Dawn De Witt said."I was so scared, yeah," said resident Pauline Huinh, who lives in the yellow house that caught fire on 23rd Avenue between Geary and Anza streets.She says her neighbor, who lives in the attic space where the fire started, banged on her door at 1:45 a.m. to warn her. "When I opened the door, so many smoke, that's it, and I told my family, ran out of the house," she said.There are three units in the house and, according to the fire department, there were hoarding conditions inside."Pretty dangerous and makes it very hard conditions to get up top. A lot of furniture in the way, very narrow attic stairwell. I think there were a lot of people living in that building," De Witt said."I've lived here for three years, so this is like my home and it's really upsetting," resident Maira McDermott said.McDermott lives in the bottom unit with three roommates. She says their upstairs neighbor in the attic told them a candle hit a curtain and started the fire."I lost a friend in the Ghost Ship fire, so this is like bringing a lot back," she said.Wind and adjacent walls also meant the fire spread to the two neighboring apartment buildings.Richmond District Supervisor, Sandra Lee Fewer, showed up at the scene Friday morning and says these type of fires are a big concern for the neighborhood. "The Richmond District has many of these homes. Wood frame, very old, a lot of them have original wiring," she said.Of the four people injured, two residents were taken to the hospital with burns and smoke inhalation. The injured firefighter cut their hand and is OK.Arson investigators are still looking into the cause of the fire.