Silver Spring Dozens of people, including three firefighters, were injured after an explosion and large fire at an apartment complex in a Maryland suburb of Washington and searchers are looking for up to seven people who were still unaccounted for, authorities said on Thursday.Firefighters were called to the four-storey apartment complex just before midnight on Wednesday and found people on upper floors who needed help, Montgomery County Fire Chief Scott Goldstein said at a briefing."People were dropping children and jumping out of other windows," Goldstein said. "Everybody was getting out of the building as rapidly as possible."About 30 people and three firefighters were injured, with the injuries ranging from minor to serious, officials said.Goldstein said natural gas furnaces and stoves are in each of the units. It took at least an hour and 45 minutes to put out the blaze and Washington Gas helped safely turn off gas, he said. About 90 people were displaced and a shelter was opened at a community centre nearby. Residents of nearby buildings that were not affected by the fire were allowed to return to their homes after several hours.Hours after the fire, smoke still was rising from the four-level garden style apartment building. Debris from the blast scattered nearly 60m, including what appeared to be an apartment door blown all the way across a two-lane road and parking lot. Brightly coloured bras hung from a tree in front of the apartments, apparently from a dresser drawer launched in the explosion. Windows across the street were broken.Firefighters were sifting through collapsed debris and a ladder truck remained extended to the building's upper levels.Some occupants and bystanders reported an explosion, spokesperson Captain Oscar Garcia.Keni Flores said she was in an adjacent building when she heard an explosion and saw the flames."I just see fire everywhere," she said. "I was thinking nobody can survive in that fire."Karina Hauffen was also in a nearby building at the time."It was a big boom, the building shook and everybody ran out," she said.Resident Willie Morales told The Washington Post he was walking across the road where the complex is located when he heard an explosion and collapsed to the ground."It was one big boom, like nothing I'd ever heard," Morales said. Then he saw flames coming from the building and banged on windows to tell people to get out.Searchers will deploy resources such as robots as they search the more unstable areas, Garcia said.A canine team searching the rubble of the apartment complex had a "hit" in one location, which could indicate someone is trapped there, Goldstein said.County officials are investigating along with the Bureau of Alcohol, Tobacco, Firearms and Explosives, Garcia said.