(Associated Press) British Airways canceled 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.”

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 6 p.m. because the two airports had become severely congested. The airline later scrapped flights from Heathrow and Gatwick for the rest of the day.

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