Computer outage grounds hundreds of British Airways flights in London

British Airways cancelled all flights from London's Heathrow and Gatwick airports on Saturday as a global IT failure upended the travel plans of tens of thousands of people on a busy U.K. holiday weekend.

The airline said it was suffering a "major IT systems failure" around the world. Chief executive Alex Cruz said "we believe the root cause was a power-supply issue and we have no evidence of any cyberattack."

He said the crash had affected "all of our check-in and operational systems."

"We are extremely sorry for the huge inconvenience this iscausing our customers and we understand how frustrating thismust be especially for families hoping to get away on holiday,"he said.

BA operates hundreds of flights from the two London airports on a typical day and both are major hubs for worldwide travel.

Several hours after problems began cropping up Saturday morning, BA suspended flights up to 5p.m. (1700 GMT) 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 and the failure of the airline's website and its mobile app. BA said the crash also affected call centres.

The airline said it was working to restore services out of Heathrow and Gatwick beginning Sunday, although there will still be some disruptions. It said it expected that London-bound long-haul flights would land on schedule Sunday.

One person 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."

Flight affected at Toronto Pearson airport

At Toronto's Pearson AirportSaturdayafternoon, British Airways staff asked travellers booked on the6:35 p.m.flight to leave the airport.

At about3:30 p.m., the staff distributed a statement saying, "Customers will not be able to rebook at the airport, through our call centres, or online, until our systems are recovered. Please do not remain at the airport."

It advised passengers requiring a hotel that they could claim "reasonable expenses."

British Airways also advised the passengers to call 1-800-AIRWAYS, the airline's phone number, to see if it had rebooked them. A recorded message on the line at4 p.m.said there would be a wait of more than 30 minutes and advised callers to use the airline's website.

Planes held on tarmac

PR executive Melissa Davis, said her BA plane was held for more than an hour and a half on the tarmac at Heathrow on a 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. The pilot said passengers on planes that have landed at Heathrow were unable to get off because there was nowhere to park.

Some BA flights were still arriving at Heathrow on Saturday, although with delays.

Busy holiday weekend

The problem comes on a bank holiday weekend, when tens of thousands of Britons and their families are travelling.

American Airlines, which operates code-share flights with BA, said it was unaffected.

"All of our flights are on time," said spokesman Ross Feinstein.

BA passengers were hit with severe delays in July and September 2016 because of problems with the airline's online check-in systems.

A union official accused BA of cutting costs by laying off IT staff last year and outsourcing the work to India.

"This could have all been avoided," said Mick Rix, national officer for aviation at the GMB union. "We can only feel genuinely sorry for the tens of thousands of passengers who are stranded at airports and face having their travel plans and holidays ruined."