British Airways cancelled all its flights from London's two main airports yesterday after a global computer system outage caused massive delays and left planes stuck on runways.
BA said there was no evidence the problem had been caused by a cyberattack.
The airline said terminals at Heathrow and Gatwick had become congested because of the IT failure and all BA flights had been cancelled.
"Please do not come to the airports. We have experienced a major IT system failure that is causing very severe disruption to our flight operations worldwide," the airline said in a statement.
"We are extremely sorry for the inconvenience this is causing our customers and we are working to resolve the situation as quickly as possible."
The problems, which passengers said had affected flights across Britain, came on a busy weekend with a public holiday on Monday and many children starting their school half-term breaks.
Last month, Germany's Lufthansa and Air France suffered a global system outage.
Passengers trying to catch planes in Britain yesterday reported long delays at check-in desks and flights being held on runways.
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