A catastrophic computer outage crippled one of the world’s busiest flight hubs on Saturday, forcing British Airways to cancel all flights out of two London airports, leaving terminals in chaos and passengers stranded.

“Today, we have experienced a major IT system failure that is causing very severe disruptions to our flight operations worldwide,” British Airways chief executive Alex Cruz said in a video message, as reports spread of errors on its website, ticket machines, baggage terminals and technical infrastructure.

Cruz wore a yellow safety vest as he spoke near Heathrow Airport — Europe’s busiest airport and major hub — where baggage piled on the floor and gate information had to be written on a whiteboard. British Airways canceled all departures at Heathrow and at nearby Gatwick Airport. Flights were supposed to resume Saturday evening, but the airline later announced that none of its planes would leave the airports before Sunday.

One passenger told the Associated Press she couldn’t transfer to another flight because “they can’t bring up our details.”

All this on one of Britain’s busiest traveling days, as the Guardian noted: at the beginning of a long weekend, as students were on a break from school.

While only British Airways departures from the two airports were directly affected, a cascade of problems rippled around the world. For example, the BBC reported, planes trying to land at Heathrow were unable to park, due to jets clogging the gates. Other outlets reported cancellations in other countries.

New York’s JFK International Airport announced delays due to the crisis, though other U.S. airport like BWI Marshall seemed to be operating normally.

But in London, an airport that flies about 200,000 people a day to and from other countries became largely dysfunctional.

One passenger, said he sat on his plane in Heathrow at for 90 minutes and that his pilot explained the technical problem was “catastrophic.”

Other stuck passengers passed the time sharing photos and videos of disorder in the terminals.

Cruz, the chief executive, said a power supply problem is believed to have triggered the crisis. A British Airways spokeswoman told The Washington Post that “there’s no evidence it’s a cyber attack.”

A trade union blamed it on layoffs and outsourcing of tech jobs, according to the AP.

“This could have all been avoided,” Mick Rix, national officer for aviation at the GMB union, told the wire service. “We can only feel genuinely sorry for the tens of thousands of passengers who are stranded at airports.”

British Airlines representatives repeatedly apologized for the problem on its Twitter account — which did not go down with the other system and thus hosted a barrage of complaints throughout the day.

Images of error messages were a common theme. The Telegraph reported that the company’s entire website went down for about two hours.

It’s hardly the first time British Airways has suffered a tech meltdown. The company’s website and online check-in system went down for at least seven hours last month, the Register reported.

Glitches caused widespread British Airway delays at the same airport on at least two occasions last year, according to Reuters. And other airlines have experienced similar problems — including a global system outage at Lufthansa and Air France, and a power surge at Delta’s headquarters in Atlanta that led to mass delays.

“We are extremely sorry for the inconvenience this is causing our customers during this busy holiday period,” an airline spokeswoman said in a statement Saturday.

The company says “most long-haul flights due to land in London tomorrow” should arrive on time, though “delays and disruption may continue.”

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Travelers stranded outside the entrance of Heathrow Airport Terminal 5 after British Airways flights were canceled Saturday. (Daniel Leal-Olivas/Agence France-Presse via Getty Images)