LONDON (REUTERS) – British Airways cancelled all its flights from London’s two biggest airports on Saturday (May 27) after a global computer system failure caused confusion and chaos, with thousands of passengers queuing for hours and planes left stuck on runways.

The failure, caused by a power supply problem, disrupted BA’s flight operations worldwide and also hit its call centres and website, said Alex Cruz, the chairman and chief executive of BA, part of Europe’s largest airline group IAG.

“All of our check-in and operational systems have been affected and we have cancelled all flights from Heathrow and Gatwick for today,” Cruz said in a video message on Twitter.

“We are extremely sorry for the huge inconvenience this is causing our customers and we understand how frustrating this must be, especially for families hoping to get away on holiday.”

He said the airline’s IT teams were working “tirelessly” to fix the problem and there was no evidence of any cyber attack.

A check by The Straits Times showed that flights at Changi Airport were unaffected. Two BA flights to London on Saturday night, BA16 and BA12, were still on schedule to take off from Changi Airport. BA16 to London left at 10.35pm, while BA12 left at 11.15pm.

"The two flights are unaffected," said a check-in staff member at the BA counter in Changi Terminal 1, adding that they would have to wait for more information from London to determine if flights would be affected today.

British PM Theresa May calls on British Airways to repair IT system, recompense customers https://t.co/1abqu6DqRh — Babblers (@Babblers_net) June 1, 2017

The problems, which passengers said had affected flights across Britain, came on a particularly busy weekend with a public holiday on Monday and many children starting their school half-term breaks.

Terminals at Heathrow and Gatwick became jammed with angry passengers, with confused BA staff unable to help as they had no access to their computers.

“It’s a complete nightmare. There’s just hundreds and thousands of people accumulating in the departures bit,” Roshni Burt, who was flying from Heathrow to Bahrain with her young son, told Reuters.

She arrived at the airport at 0730 GMT (3-30pm Singapore time), queued for hours at the check-in, where the baggage drop-off system stopped working, and then waited at the departure gate for two hours until passengers were told the flight was cancelled.

All the affected passengers were corralled through a single gate so they could go back through border checks and then re-book flights.

'MASSIVE SCRUM'

“We are now in a massive scrum trying to get to this gate. BA staff didn’t know what’s going on,” Burt said. “Border control aren’t going to be able to deal with all these people. I don’t know what’s going to happen.”

BA is the latest airline to be hit by computer problems. Last month Germany’s Lufthansa and Air France suffered a global system outage which prevented them from boarding passengers.

In September last year BA apologised to passengers for check-in delays caused by operational glitches that delayed flights at Gatwick and Heathrow, in a repeat of a similar incident that affected London-area flights for the airline last July.

In August a power surge near US airline Delta’s Atlanta headquarters caused computers to crash and led to widespread delays across Delta’s entire network.

BA said it would try to get affected customers onto the next available flight although the re-booking process was being hindered by the system problems. Those unable to fly would get a full refund, Cruz said.

“We hope to be able to operate some long-haul inbound flights tonight, which will land in London tomorrow,” he said. “We are extremely sorry for the inconvenience this is causing our customers during this busy holiday period.”

Some passengers said they had boarded flights but were then left stuck on the runway.

“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.

Another, journalist Martyn Kent, wrote: “Sat on plane at Heathrow for hour and a half now. @British–Airways Captain describes IT problem as ‘catastrophic’.”

T5 @British_Airways passengers not going anywhere. Apparently a worldwide computer issue. Not much of a start to the half term hols... pic.twitter.com/zpUd0PB4yE — Jonathan Samuels (@jonathansamuels) May 27, 2017

we are waiting at our gate. No sign of boarding. Prepare for big delays. Baggage system down also. — Roshni Burt (@RoshniBurt1) May 27, 2017

#heathrow @HeathrowAirport Not a single customer announcement. Been queuing for 1 hour. What is going On? Keep us informed. pic.twitter.com/v6aEU0n6yo — Jodi Rilot (@jodirilot) May 27, 2017

Hey @British_Airways, couldn't log in to the app with my boarding pass on because systems were down and I missed my flight. What can I do? — Henry Tail (@unexpectedtails) May 27, 2017

British airways computers down T5 and standstill, stranded on the plane and they make us pay for food!!

Please retweet this indicency! — nadia whittley (@naolge) May 27, 2017

We are on the runway.. For hour now..no offer of drinks..and because ba only takes cards now, we only have cash...wat we supposed to do!!?? — Julie adie (@Julieadie1) May 27, 2017

Heathrow, one of the world’s busiest airports, said in a statement: “We are working closely with the airline to assist passengers who have been affected by the British Airways issue and have extra customer service colleagues in terminals to assist those passengers already at Heathrow.”

In February IAG reported its annual operating profit rose 8.6 per cent to 2.5 billion euros and said its British Airways transatlantic business, based at Heathrow, had held up well compared with Europe’s highly competitive budget market.