A man and woman were killed early this morning in a fiery tractor-trailer crash in Greenfield, according to State Police. State troopers responded to a report of a tractor-trailer that crashed into the median on Route 91 North between exits 27 and 28 at 3:00 a.m. Upon their arrival, the vehicle was fully engulfed in flames, State Police spokesman David Procopio said. A trooper attempted to approach the tractor-trailer to assist the occupants, but was driven back by increasing fire and explosions, according to Procopio. State Police have tentatively identified the man and woman discovered in the cab of the vehicle and believe both are from out of state. They did not disclose their identities. The cause of the crash is under investigation.