Thousands of British Airways passengers are facing "total chaos" due to a "systems issue".
Frustrated holidaymakers have been stuck on board planes for hours due to severe disruption at airports across the UK, including Heathrow, Gatwick and Glasgow, and in Italy.
Flights from George Best Belfast City Airport to London airports are also affected by the delays.
Holidaymakers told how their getaways have been thrown in doubt and some passengers became so frustrated they just walked off planes and gave up, the Mirror reports .
BA confirmed it was experiencing "systems problems" which were affecting the check-in process - including its app - and delaying flight departures.
The airline is using back-up and manual systems to try and cope with the failure, but it was unknown when the problem would be resolved and operations would return to normal.
A British Airways spokesperson said: "We are working as quickly as possible to resolve a systems issue which has resulted in some short-haul cancellations and delays from London airports.
"A number of flights continue to operate but we are advising customers to check ba.com for the latest flight information before coming to the airport.
"We are offering customers booked on short-haul services departing from Heathrow, Gatwick and London City today, the opportunity to rebook to another day.
"We are encouraging customers to check ba.com for the latest flight information, and to allow additional time at the airport."
Zac Lennie was stuck on a plane with his children for more than an hour with no idea when they would leave Gatwick.
He told Mirror Online : "We arrived at 4.30am for a 6.45am flight to massive queues. We were told there was a system failure.
"It took an hour and 15 minutes before we got through security and we had to go straight to the gate.
"They boarded us as normal, but 15 minutes after we were due to take off we were told the systems had gone down and we were awaiting paperwork.
"Thirty minutes later we were told the same. Now we’ve just been told we have our paperwork and we will possibly get to take off if we can get a slot, but we're currently on standstill with the plane door open.
"The staff are good, they're in a s*** position. There are a lot of families on my flight. Kids are getting very restless."
Another passenger, Michael, was stranded on a plane at Newcastle Airport while en route to Slovenia with a bride and groom who are getting married on Saturday.
He said: "The cabin crew on board have said it's a system failure in regards to the load sheets to allocate baggage and weight distribution for the trim [centre of gravity].
"One cabin crew said the system had been down since they arrived for duty approximately 5.15am, but still boarded the passengers.
"The captain said over the intercom it is a global failure and no aircraft were moving due to the essential data required.
"We're two hours and ten minutes past our departure time. No movement here."
He said flight attendants were giving updates and handing out drinks, but passengers' bags had not yet been loaded.
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