Officials in hazmat suits were forced to remove a man from a Ryanair flight after he received a text message to say he had tested positive for coronavirus.
The passenger and his travel companion were taken off the plane before it left Stansted on Wednesday evening, the airline said.
The pair were on the aircraft for less than 10 minutes, but caused the Pisa-bound plane to be delayed by one hour and 20 minutes, a spokesman added.
Their seats and overhead cabins were disinfected while they were taken to an isolation area at the airport.
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Video footage of the incident showed firemen dressed in hazmat suits at the front of the plane, with passengers watching in horror from their seats.
One passenger told Sky News it was “frighteningly real” and he and his mother wanted to get off – but weren’t allowed.
Fionn Murphy was travelling to Pisa with his mother, who was seated separately from him on the flight.
He told Sky News: “After half an hour I was wondering why we hadn’t moved. We then saw the fire brigade pull up outside the plane.
“Two men exited the fire truck and put on full body suits and began to board the plane. It was clear something dramatic was unfolding.”
Mr Murphy said he and his mother were desperate to get off the plane, “but were not given that option”.
He added: “At this point we started to feel a bit panicked, not knowing if the flight would be cancelled, or worse we’d been exposed to the virus.
“Once the men came on in hazmat suits it got frighteningly real. I wanted to get off the flight straight away.”
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A Ryanair spokesman said: “A passenger who boarded a flight from London Stansted to Pisa on 26 August received a text message notification before departure that he had tested positive for COVID-19.
“There was little if any risk of coronavirus transmission to other passengers or crew members as all of whom were also wearing face masks at all times.
“The aircraft departed for Pisa following a delay of one hour and 20 minutes to allow for the empty seats and overhead cabin bins to be disinfected to comply with all UK health authority guidance. Ryanair apologises to all passengers for this short delay.”
A Stansted spokesman told Sky News the two passengers were removed by the local fire service after being alerted by Ryanair.
Public Health England workers oversaw their onward journey, they added.