 London (CNN) British Airways canceled all Saturday flights from London's two biggest airports after "a major IT system failure" caused severe disruption to flight operations worldwide, the airline said. In a video statement released via Twitter, he added: "I am really sorry we don't have better news as yet, but I can assure you our teams are working as hard as they can to resolve these issues." "We believe the root cause was a power supply issue and we have no evidence of any cyberattack." The airline, which had previously said flights would be cancelled until 18:00 BST, has now cancelled all flights for Saturday and asked passengers not to come to Gatwick or Heathrow airports. All passengers affected by the failure - which coincides with the first weekend of the half-term holiday for many in the UK - will be offered the option of rescheduling or a refund. Media playback is unsupported on your device Media caption Queues at Heathrow airport stretched out of the terminal 
 
 Serious problems with British Airways' IT systems have led to thousands of passengers having their plans disrupted, after all flights from Heathrow and Gatwick were cancelled. Airline workers 'totally crippled' 
 
 Travelers in the United Kingdom were already reporting disruptions, including baggage and flight delays, when the airline reported serious computer problems around midday. Passengers described "chaotic" scenes at the airports, with some criticising BA for a lack of information. EU flight delay rights 
 
 Image copyright @TimReidCE Image caption Passengers have experienced large queues and disruption at Heathrow Terminal 5, British Airways' main London terminal If planes cannot take off, they cannot leave gaps at the gate for others to land. "Eventually after sitting on the tarmac for one and a half hours we disembarked the plane. It continues... #britishairways #heathrowdelays — Philip Bloom (@PhilipBloom) May 27, 2017 
 
 Filmmaker Philip Bloom tweeted that he was stuck on the tarmac at Heathrow after his delayed flight from Belfast, Northern Ireland, finally landed because there was no space for the aircraft to park. I docume... https://t.co/aYNq2qVvlo pic.twitter.com/HZ52FRbSjl — Philip Bloom (@PhilipBloom) May 27, 2017 
 
 Bloom later tweeted, "9 hours after checking in at Belfast airport we get home after the chaos of the British Airways IT crash."
– British Airways canceled all flights out of London's two largest airports Saturday—the first day of a spring bank holiday weekend in Britain—affecting tens of thousands of travelers. The problem stems from British Airway's IT system, the entirety of which apparently crashed worldwide, the AP reports. According to CNN, the airline says it doesn't appear to have been a cyberattack, but rather a "power supply issue." An aviation expert tells the BBC that British Airways "can't do anything at all." That includes having planes take off, moving baggage, and issuing credentials to passengers. The problem affected call centers, the British Airways website, and its mobile app. While British Airways hopes to have some flights in the air Sunday, the problem could persist for days, one expert says. On a normal day, British Airways has hundreds of flights out of Heathrow and Gatwick. On Saturday, travelers described chaos at the airports. One such traveler at Heathrow called it one of "most turbulent, badly organized days that I've ever experienced in Britain." With planes unable to take off and blocking gates, passengers on flights arriving at the airports were unable to disembark. Some waited on their planes for four hours only to get off and learn they had no idea where their luggage was. British Airways eventually told passengers to stop coming to the airport. Those affected will be offered a rescheduled flight or refund.