Both runways were closed at Heathrow Airport after a British Airways (BA) plane made an emergency landing, the airport has said.
All passengers and crew were "safely evacuated" from the plane following an engine fire at about 09:00 BST.
In a statement, BA said: "The BA762, Heathrow to Oslo service, returned back to Heathrow shortly after take-off due to a technical fault."
The southern runway has re-opened. The northern runway remains closed.
BA said the Airbus A319 was carrying 75 passengers - who were safely evacuated - and a "full investigation" would be conducted into the incident.
John Coghlan told the BBC he saw a "black smoke trail" from the engine of a British Airways Airbus A319.
He said: "[It was a] safe landing and passengers evacuated by chutes on runway."
Jez Stamp, from Farnham in Surrey, who was on a plane waiting to take off to Jordan, said: "I could see smoke on the right engine.
"We just saw it come to a halt and fire engines were already there waiting for it and they immediately started hosing the plane down."
London Fire Brigade tweeted: "One crew from Heathrow fire station is assisting Heathrow Airport's fire service with an aircraft fire.
"We believe the fire is now out."
-BBC
