The nature of the emergency is not immediately clear. However, some images from the scene show smoke emerging from the back of the plane.
Footage captured from a passenger on board a nearby plane shows people exiting the affected flight via its rear slide.
The evacuated flight was American Airlines Flight 731, due to leave London Heathrow at 1.30pm local time, and arrive at Charlotte Douglas International Airport in North Carolina at 5.20pm local time.
Other photos from the scene show emergency personnel and fire services surrounding the aircraft.