A fire in a smoke shop cause an explosion and spread to nearby structures on Saturday evening in the Los Angeles city centre, injuring eleven firefighters. Crews had entered the building to battle what was initially thought to be a minor blaze when they noticed that the smoke pressure was increasing, and decided to evacuate, Los Angeles Fire Department chief Ralph Terrazas said. He said the blast occurred as the firefighters were leaving the building from the roof and the ground floor. The Los Angeles Fire Department's Capt Erik Scott said "one significant explosion" shook the neighbourhood at about 6.30pm. Firefighters inside had to run through a wall of flames he estimated was 9 metres high and wide, and those on the roof scrambled down a ladder that was engulfed in fire. Capt Scott said people at the scene described the explosion as sounding like a freight train or jet engine. Some of the fleeing firefighters were on fire and tore off their protective equipment and left it on the pavement along with melted helmets, Capt Scott said. "That was one of the worst scenes I've seen," he said. All 11 firefighters suffered burns, from minor to serious. Three were listed as in critical condition, and two were on ventilators. All were expected to survive. “The good news is everybody’s going to make it,” Mayor Eric Garcetti said at a news conference outside the Los Angeles County-University of Southern California Medical Centre, where all the injured were treated. “Things could have been so much worse,” said Los Angeles Fire Department Medical Director Dr Marc Eckstein, who works at the hospital and helped treat the injured. Mr Terrazas said firefighters saw butane canisters inside the building and outside on the street but it was not known what caused the blaze. "Everything is under investigation by our arson team. All I can say at this point is that the cause is under investigation," he said. About 230 responders battled the fire as it spread to other buildings in the area before it was extinguished about two hours after it began. Fire officials said the building where the blast occurred housed a business – Smoke Totes Wholesale Distribution – that sold smoking and vaping paraphernalia and supplied other businesses that make "butane honey oil". Honey oil is a resin made from marijuana, and its production involves extremely flammable chemicals. Several storefronts in the area were blackened by the force of the blast, and a fire engine had a scorched roof and was covered with debris. Thick smoke from the blaze was visible from kilometres away.