(CNN) A British Airways flight from London to Spain was evacuated after smoke filled the cabin moments before the flight was due to land.

Passengers said that the incident -- which occurred on Monday -- was "terrifying" and felt like a "horror film", with travelers shouting that they were unable to breathe.

British Airways confirmed a "technical issue" on flight BA422, which was traveling from London Heathrow to Valencia on Monday afternoon, and said passengers were evacuated from the aircraft.

The BA flight was traveling from London to the Spanish city of Valencia

One traveler on board, Lucy Brown, told CNN that the smoke had been thick with a metallic, chemical odour, adding: "We covered our mouths with our clothes. We don't know why oxygen masks didn't deploy."

"Passengers started shouting they couldn't breathe," she said.

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