Passengers escaped from an American Airlines plane down an emergency slide at Heathrow Airport following a "technical issue".
Footage showed passengers, including children, disembarking via a slide towards the runway at the rear of the aircraft at Terminal 3.
Airport fire crews were dispatched to the aircraft, but no-one appeared to be injured during the alert on Sunday morning, according to an eye-witness.
Ross Hiscock, 28, was on a flight which had arrived at Heathrow from Helsinki when he saw smoke coming from the tail-end of the plane next to his.
He said: "I saw a lot of smoke come out from the tail-end of the aircraft. I wondered if it was normal, whether it was just exhaust fumes.
"Then the door opened on the right side of the aircraft and crews deployed slides from the rear and the middle of the plane.
"Next we wondered whether it was a drill, but then we saw they were real passengers. I saw at least one carrying a child.
"It all happened in a matter of seconds. Everyone seemed to be okay."
A Heathrow Airport spokeswoman said a "technical issue" was identified with the aircraft and the problem was resolved.