A British Airways flight has been evacuated after smoke filled the cabin shortly before landing.
The airline confirmed an “incident” on flight BA422 which departed London Heathrow at 15:10 BST on Monday and has now landed in Valencia.
Passenger Rachel Jupp, who was with her children, told BBC News smoke filled the cabin “very quickly” about 10 minutes before its scheduled landing.
BA has apologised to passengers on board the aircraft, an Airbus A321.
It added that its staff were assisting customers in the airport terminal.
Ms Jupp, the editor of BBC Panorama, said there was no official announcement about what was happening as white smoke appeared to come through the air conditioning system into the cabin.
“Very quickly, you couldn’t see the passengers two seats down from you,” she said.
‘Told to run’
As the plane began to descend quickly Ms Jupp said she heard calls to “get down” in order to breathe the cleaner air near the floor of the aircraft.
She said the pilot did a “really good job” to make a “pretty smooth landing”.
“We later found out the cockpit was full of smoke and he had a gas mask on,” she added.
Ms Jupp said cabin staff were unable to open the emergency exits for “three or four minutes” after the plane landed.
Passengers then slid down the emergency chutes to the runway.
As members of the emergency services ran towards the plane, Ms Jupp said: “We were just told to run and get as far away as we could from the plane.”
‘Like a horror film’
Pictures have emerged on Twitter of what appears to be the plane cabin filled with smoke.
Passenger Lucy Brown tweeted that the “terrifying” experience felt like a “horror film”.
A BBC producer at Valencia airport was told by a member of staff on the ground that there was a “fire in the motor” of the plane.
Gayle Fitzpatrick, from Glasgow, told PA fire crews were waiting on the runway when the plane landed and passengers were directed to the terminal.
Mrs Fitzpatrick, who was on holiday with her husband Stephen, added: “There were no communications from the crew, some of which started to wear full oxygen masks and protective fire wear.”
She added: “People were crying and hyperventilating. It was genuinely scary.”
In an email to affected passengers British Airways said it was “sourcing an alternative aircraft” to operate flights back to London.
Travellers who have been delayed overnight have been given free accommodation at a local hotel, BBC News has been told.