United Express Flight 5365, operated by SkyWest, was preparing to depart LAX en route to Salt Lake City shortly after 7 p.m. when then incident occurred.
The Embraer 175 aircraft "was taxiing away from the gate area when a male passenger onboard opened the door of the aircraft and exited onto the taxiway," Los Angeles Airport Police said in a statement. Officers and the Los Angeles Fire Department, and later the FBI, responded to the scene.
The FBI said the passenger pounded on the cockpit door before he exited the plane through an emergency door.
The man was treated for unspecified injuries and was transported to a hospital in unknown condition. His identity was not released.
No one else was hurt, and the airplane was able to make its way back to the gate area, police said.
An arrest was not immediately announced.
DEVELOPING: More details will be added to this report as they become available.