British Airways have apologised as holidaymakers face disruption due to a system problem on Saturday morning.
It comes as many Britons head overseas for the Bank Holiday weekend and half-term school break.
A spokeswoman for the airline said: “We apologise to customers who are facing some delays following an IT outage this morning.
“We are working to resolve the problem as quickly as possible.”
BA’s website is currently unavailable and some travellers have said they were unable to check in on the airline’s mobile app.
Some people have taken to social media to vent their frustration at the issues they have been experiencing.
One passenger, Henry Tail, tweeted that he has missed his flight as a result.
Another, Philip Bloom, posted: “Stuck on a @British_Airways plane at Belfast going nowhere. “BA computers down worldwide” whatever that means! #britishairways”
Gareth Wharton, who is at Heathrow Terminal 5, tweeted a picture of BA staff writing gate information on a whiteboard amid the systems outage.
“Gets worse, #T5 staff having to put gate info up on a white board #LowFi #Heathrow,” he wrote.
Julie Adie wrote: “We are on the runway.. For hour now..no offer of drinks..and because ba only takes cards now, we only have cash…wat we supposed to do!!?? (SIC)”
It comes a day after passengers at Gatwick Airport faced long queues due to a baggage system problem.
Those taking flights on Friday were forced to travel without their hold bags and were asked to carry any essential items in their hand luggage.