The emergency slides have been activated on an American Airlines flight at Heathrow Terminal 3, reportedly due to smoke in the cabin.
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. No injuries have been reported from the incident.
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.
While some nearby flights have been delayed by the emergency evacuation, others are continuing to arrive at and depart from Terminal 3.