A global technology failure at British Airways led to delays, airport congestion and flight cancellations for thousands of customers at London-area airports on Saturday.

The problems began around 7 a.m. local time. By late afternoon, the airline had canceled all Saturday flights departing from Heathrow and Gatwick airports. In a statement, it cited “a major I.T. system failure that is causing severe disruption to our flight operations worldwide.”

The glitch affected the airline’s check-in and operational systems, including call centers, the airline’s chief executive, Alex Cruz, said in a video on Saturday.