( CNN ) -- At least six people were dead and one critically injured Sunday after a midair crash between two medical helicopters near a hospital in Arizona , authorities said . Rescue workers sift through wreckage from two medical helicopters that collided midair Sunday afternoon . The collision , at Flagstaff Medical Center in Flagstaff , Arizona , set fire to a 10-acre area , according to fire officials , and another two rescue workers were injured by a secondary explosion after the crash . The helicopters collided at roughly 3:45 p.m. local time , according to the Federal Aviation Administration . `` As you can imagine , we 've got lots of heaps of metal to go through , '' said Capt . Mark Johnson of the Flagstaff Fire Department . `` It 's just difficult right now . '' He said a landing pad on the roof of the hospital is used by medical helicopters . Federal Aviation Authority officials originally had reported at least seven deaths and three critical injuries , but they revised those numbers after investigators spent more time on the scene . Flagstaff Police Department Sgt . Tom Boughner said the two rescue workers were not immediately believed to be seriously injured . He said the helicopters crashed into a wooded area near a neighborhood and that no one on the ground was believed to have been injured or killed in the crash . He said the fire had been contained by Sunday evening . FAA spokesman Ian Gregor said at least one of those killed in the collision was a patient . He said three of those killed , including the patient , were aboard a Bell 407 helicopter operated by Air Methods Corporation , an air medical service provider . The other helicopter , operated by Classic Helicopter Service of Utah , also was a Bell 407 . The other four victims , including the one critically injured , were on that helicopter . Both helicopters were headed to the hospital at the time of the crash , Gregor said . FAA safety inspectors from Phoenix , Arizona , were en route to the scene Sunday , and additional inspectors from Washington were expected to arrive Monday morning . The National Transportation Safety Board will lead a probe into the crash , Gregor said .
NEW : The killed includes one seriously ; one critically injured . Collision sets fire to an area near Arizona 's Regional Medical Center . ` ` We ' ve got lots of heaps of metal to get through , '' fire captain says .