British Airways canceled all flights from London's Heathrow and Gatwick airports Saturday as a global IT failure caused severe disruption for travelers on a busy holiday weekend.
The airline said it was suffering a "major IT systems failure" around the world. It didn't say what was causing the problem but said there was no evidence of a cyberattack.
Several hours after problems began cropping up Saturday morning, BA suspended flights up to 6 p.m. (1700GMT) because the two airports had become severely congested. The airline later scrapped flights from Heathrow and Gatwick for the rest of the day.
Passengers at Heathrow reported long lines at check-in counters, flight delays and failures of BA's website and mobile app.
One posted a picture on Twitter of BA staff writing gate numbers on a white board.
"We've tried all of the self-check-in machines. None were working, apart from one," said Terry Page, booked on a flight to Texas. "There was a huge queue for it and it later transpired that it didn't actually work, but you didn't discover that until you got to the front."
Another traveler, PR executive Melissa Davis, said she was held for more than an hour and a half on the tarmac at Heathrow aboard a BA flight arriving from Belfast.
She said passengers had been told they could not transfer to other flights because "they can't bring up our details."
Passenger Phillip Norton tweeted video of an announcement from a pilot to passengers at Rome's Fiumicino airport, saying the problem affects the system that regulates what passengers and baggage go on which aircraft. He said passengers on planes that have landed at Heathrow were unable to get off because there was nowhere to park.
Heathrow said the IT problem had caused "some delays for passengers" and it was working with BA to resolve it. Some BA flights were still arriving at Heathrow Saturday afternoon, while many were listed as "delayed."
The problem comes on a holiday weekend, when thousands of Britons are travelling.
BA passengers were hit with severe delays in July and September 2016 because of problems with the airline's online check-in systems.