British Airways has cancelled all flights from London's Heathrow and Gatwick airports for the rest of the day due to a "global system outage".
Passengers have faced delays and long waits for what the airline called a "major IT system failure that is causing very severe disruption to our flight operations worldwide".
BA says there was no evidence of a cyberattack. Chief executive Alex Cruz, in a video posted on Twitter, said a power supply issue was to blame for the computer system failure.
The airlines said delays could continue into Sunday, but most long-haul flights should be able to land as normal in London
Passengers were complaining about not being able to use the airlines' website or the app which is causing them to miss their flights.
The disruption comes at the start of a bank holiday weekend and during half-term school holidays in the UK.
British Airways said in a statement "We apologise for the current IT systems outage. We are working to resolve the problem as quickly as possible."