A medical helicopter crashed Saturday night at the Far South Side in Chicago.
In particular, a patient airliner helicopter, in which four people were riding, at around 21:15 in the evening, crashed near highways.
The crash injured all four occupants, one of whom was the pilot, two crew members and a patient.
The injured were taken to hospital.
According to the Chicago Fire Department, one of the injured is in critical condition in hospital and the other three are in serious condition.
The cause of the helicopter crash was not known.
Federal Aviation Authority officials are in the process of investigating the cause of the crash.