British Airways said it had canceled all flights from London’s Heathrow and Gatwick airports scheduled before 1700 GMT on Saturday due to a global computer outage.
The airline said that flights will not resume for the remainder of the day. Most long-haul flights due to come to the airports on Sunday would arrive as expected but there would be further delays and disruption to its services.
“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.
British Airways said on Saturday there was no evidence that a global breakdown of its IT systems had been caused by a cyber attack.
WATCH: British Airways cancellation spoils passenger’s trip to Greece
Because of the blackout, British airways says that flights were delayed on Saturday, with passengers reporting massive hold-ups at airports and planes being held on runways.
The problems, which passengers said were affecting flights across the country, came on a particularly busy weekend in Britain with a public holiday on Monday and many children starting their school half-term breaks.
“We apologize to customers who are facing some delays following an IT outage this morning,” a BA spokeswoman said. “We are working to resolve the problem as quickly as possible.”
She gave no further details. Passengers on social media reported long delays at check-in desks and flights being held on runways.
“Still on the tarmac at Leeds. #britishairways reckon Heathrow is so backed up we can’t set off. No way we’ll make our Vegas flight,” one passenger David Raine wrote on Twitter.
WATCH: Video shows massive lines after British Airways cancels flights at Heathrow, Gatwick
Another, journalist Martyn Kent, wrote: “Sat on plane at Heathrow for hour and a half now. @British_Airways Captain describes IT problem as ‘catastrophic’.”
London’s Heathrow Airport, one of the world’s busiest, said it was working with BA and advised passengers to check their flight status before traveling.
Passenger Roshni Burt, who was flying from Heathrow to Bahrain with her young son, said there was no news about when her flight would depart.
“When we left the check-in area there were angry people, people getting frustrated that their flights were coming up or near to departure, people getting turned away … with BA staff basically saying ‘if you’ve not checked in online, you’ve missed your flight’,” she told Sky News.
BA is the latest airline to be hit by computer problems. Last month Lufthansa and Air France suffered a global system outage which prevented them from boarding passengers.