Firefighters responded to a possible hazardous materials incident at Heathrow Airport.
Specialist crews were deployed to carry out an assessment of the scene, and Terminal 4 check-in was evacuated as a precaution whilst firefighters conducted operations. Around 20 people have been assessed on scene by paramedics from the London Ambulance Service.
The Brigade was first called about the incident at 1701, with crews from Feltham, Heathrow, Wembley and surrounding fire stations mobilised to the scene.
The cause of the incident remains under investigation at this time.