( CNN ) -- Heavy winds from a severe storm caused significant damage , shattered windows and sent debris raining down on passengers at an airport in St. Louis Friday night . The Lambert-St. Louis International Airport is closed indefinitely while officials investigate the damage , St. Louis Mayor Francis Slay told reporters . `` There was a reported sighting of a tornado . Although that has not been confirmed , that storm caused significant damage to the airport , '' he said . The reported tornado twisted metal and blew out plate-glass windows in the airport 's main terminal , CNN affiliate KSDK reported . Four people were transported to nearby hospitals with injuries , Slay said . Passengers were hit with flying glass and debris as winds ripped off part of the roof in the airport 's C concourse , the station reported . One witness described a chaotic scene outside the terminal as officials evacuated passengers from at least one aircraft . `` The plane was rocking back and forth , '' said Brett Knewitz of Albuquerque , New Mexico , who was on a plane that was about to take off from the airport when the storm hit . Initially officials did not allow evacuated passengers into the airport , he said , because of concerns that the building 's roof would collapse.Once he was allowed inside , Knewitz said he saw an injured gate agent . `` She was bleeding like crazy , '' he said . Concourse C is used by American Airlines , AirTran and Cape Air , airport spokesman Jeff Lea said . The National Weather Service said witnesses believe a tornado was on the ground for several miles and observed the twister from a tower at the airport . KSDK reported that the storm also blew the steeple off a church and forced authorities to close highways . CNN 's Marlena Baldacci , Taylor Ward and Greg Morrison contributed to this report .
NEW : The St Louis mayor says the airport is closed indefinitely . ` ` The plane was rocking back and forth , '' one witness says . CNN affiliate KSDK : The tornado ripped off part of a wing at one point . Passengers are hit with flying debris and debris , KSDK says .