Terrified passengers were forced to evacuate a plane after it filled up with smoke mid-flight.
One person on board the trip from London Heathrow to Valencia described the scene as being like a "horror film".
Shocking footage from inside the aircraft showed it fill with thick smoke before it landed in the Spanish city, where passengers were then seen exiting via inflatable slides.
Gayle Fitzpatrick, who was on the flight, told the Standard: "It was very scary. The flight was just ending, and with ten minutes to go the flight started descending rapidly as smoke started to fill the cabin.
"A detector was going off saying the cabin was filling with smoke. It was like a horrible white acrid smoke."
She said staff opened emergency doors when the flight landed and passengers were told to exit down the chutes.
Ms Fitzpatrick added: "There were fire engines waiting and then we were all ushered into a bus then to the airport. We are still waiting to hear what happened. People were crying and hyperventilating. It was genuinely scary."
Another passenger, taking to social media, said: "Terrifying experience on flight to Valencia. Felt like horror film. Thankfully everyone safe. Flight filled with smoke and had to be emergency evacuated."
It was described as "the most terrifying experience of my life" by another person on board.
Three people were treated for smoke inhalation and 16 passengers were treated for anxiety and chafing suffered when they slid down inflatable emergency slides, according to the Europa Press news agency.
Mrs Fitzpatrick claimed passengers had been stuck at the airport for at least two hours "without any information at all".
She said groups of people had since been told they could go and collect items from the plane.
A statement from British Airways said: "We can confirm that British Airways flight BA422 from Heathrow to Valencia has been involved in an incident today.
"The aircraft, an A321, has landed and all customers and crew have disembarked.
"British Airways teams are assisting customers who are in the airport terminal."
