( CNN ) -- Firefighters were battling a gas line or gas-fueled blaze Thursday evening that engulfed dozens of homes and sent bright flames and huge plumes of smoke shooting hundreds of feet into the air in a neighborhood in San Bruno , California , emergency management officials said . `` The flames are being fueled by something , '' said Kelly Huston of California Emergency Management . `` There was a loud explosion being reported by witness and just dozens of homes on fire '' He said there were some injured and walking wounded after the fire , which started around 7 p.m. ( 10 p.m . ET ) . `` Crews are just trying to assess how many injuries they have there and what they 're going to do to contain the flames , '' Huston said . Investigators were still trying to determine what caused the fire . `` It was a gas station explosion , or a pipeline close to a gas station , '' said Jay Alan , a spokesman for California Emergency Management , citing informationg from the San Bruno Police Department . Authorities are worried about winds that could spread the fire and embers that are falling on adjacent houses , he said . Helicopters were dropping retardant on homes to try to stop the fire 's spread . They are still assessing the area and trying to determine how many people are injured , he said . `` It 's still very much an unfolding incident as we speak , '' he said . CNN affiliate KGO reported that people as far as a half-mile away said they felt the boom and heat of the explosion . An evacuation center has been set up and the Red Cross is heading to the scene to provide aid to residents , KGO said . Church of Highlands Staff Pastor Leigh Bishop told CNN he witnessed a `` devastating explosion '' that caused the fast-moving fire . Bishop said two people from his church had lost their homes and at least one person had burn injuries . Kaiser Permanente South San Francisco hospital received three people in ambulances and four walk-ins with injuries from the fire , Administrative Services Director Nida Winnett said . Six of those people were in the hospital 's intensive care unit , and three of them are suffering from burns , Winnett said . Seton Medical Center spokeswoman Beth Nikels said three people with injuries from the fire came to the hospital , and one is being transported to a burn center . California 's state fire department is sending 25 fire engines to the area to help battle the blaze at the request of the local fire department , spokesman Daniel Berlant said . The fire is in a populated area about two miles west of San Francisco International Airport , Huston said . All flights and operations there were normal Thursday evening , airport spokesman Michael Brown said . At least 5,000 customers are without electricity , KGO reported . `` I will be closely monitoring the situation with the California Emergency Management Agency and will ensure a swift investigation begins to determine the causes , '' California Lt. Gov . Abel Maldonado said in a statement . CNN 's Ninette Sosa , Shawn Nottingham , Anderson Cooper , Karan Olson , Sonya Hamasaki and Deanna Proeller contributed to this report .
NEW : An evacuation plan has been set up . Hospital officials say patients have arrived with minor injuries . The fire is about 20 miles from San Francisco International Airport . Helicopters are dropping bombs on houses to stop its spread .