Thousands of British Airways passengers are still facing long lines, confusion and cancelled flights as the airline works to restore its computer systems after a global IT failure crippled its services.

BA cancelled all flights from Heathrow and Gatwick Saturday after the IT outage, which it blamed on a power-supply problem. The glitch threw the plans of thousands of travellers into disarray, on what is a holiday weekend in Britain.

The airline said that it hoped to operate a "near normal schedule" at Gatwick and the "majority of services" from Heathrow on Sunday (28 May), a day after cancelling all flights from both London airports.

"Work continues to restore all of our IT systems but we expect some further disruption today," BA said in a statement.

Passengers – some of whom had spent the night at the airport – faced long lines to check in, re-book or find lost luggage on Sunday, as temperatures soared in southern England, and dozens more flights from Heathrow were cancelled.

BA delays
Thousands of passengers face a second day of travel disruption after a British Airways IT failure caused the airline to cancel most of its services Reuters
BA delays
Thousands of passengers face a second day of travel disruption after a British Airways IT failure caused the airline to cancel most of its services Reuters
BA delays
Thousands of passengers face a second day of travel disruption after a British Airways IT failure caused the airline to cancel most of its services Reuters
BA delays
Thousands of passengers face a second day of travel disruption after a British Airways IT failure caused the airline to cancel most of its services Reuters

"Everyone is upset. There's people in tears," said Melanie Ware, who flew in from Los Angeles and was trying to get to Venice on her honeymoon.

"We rebooked for Venice for tonight, which they also have cancelled now," she told Sky News. "So we have no way of getting out of Heathrow and they haven't compensated us for anything, and we're stuck and this is the worst honeymoon ever.

"British Airways has ruined our honeymoon."

BA delays
Thousands of passengers face a second day of travel disruption after a British Airways IT failure caused the airline to cancel most of its services Getty
BA delays
Thousands of passengers face a second day of travel disruption after a British Airways IT failure caused the airline to cancel most of its services Getty
BA delays
Thousands of passengers face a second day of travel disruption after a British Airways IT failure caused the airline to cancel most of its services Reuters

Tonda Sallee, who was trying to fly to Frankfurt, said she been in line for five hours, "and we have no idea how long we'll be in line. The rest of the day I'm sure, and we probably won't fly out today either".

Many passengers complained about a lack of information from the airline.

"Some 80-year-old lady was standing around waiting for announcements, etcetera, and she fell over," said Londoner Terry Page, who managed to get on one of the last flights from Heathrow to Dallas-Fort Worth on Saturday. He and other passengers arrived, but their luggage did not.

"We helped her up and she said 'I'm just so tired,'" Page said. "It's been a terrible, terrible day."

BA delays
Thousands of passengers face a second day of travel disruption after a British Airways IT failure caused the airline to cancel most of its services Getty
british airways delays
Thousands of passengers face a second day of travel disruption after a British Airways IT failure caused the airline to cancel most of its services Reuters
BA delays
Thousands of passengers face a second day of travel disruption after a British Airways IT failure caused the airline to cancel most of its services Getty

While not that frequent, when airline outages do happen, the effects are widespread, high-profile and can hit travellers across the globe.

BA passengers were hit with severe delays in July and September 2016 because of problems with the airline's online check-in systems.

In August 2016, Delta planes around the world were grounded when an electrical component failed and led to a shutdown of the transformer that provides power to the airline's data centre. Delta said it lost $100 million in revenue as a result of the outage.