Thousands of angry British Airways passengers on Sunday confronted long lines, confusion and canceled flights at London's Heathrow and Gatwick airports as the airline worked to fix computer systems crippled by a massive global IT failure.

British Airways said Sunday that it was still working on the massive problem, which caused the airline to cancel all flights from the two London airports.

"Work continues to restore all of our IT systems, but we expect some further disruption today," the airline said.

The airline said that it hoped to operate a "near normal schedule" at Gatwick and the "majority of services" from Heathrow on Sunday.

Saturday's cancellations upended the travel plans of tens of thousands of people on a busy holiday weekend.

The airline offered to refund or rebook customers affected by the problem.

The airline operates hundreds of flights from Heathrow and Gatwick on a typical day — and both are major hubs for worldwide travel.

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. Dozens more flights from Heathrow were canceled.

"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 canceled 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."

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, et cetera, 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."

A British Airways official told Fox News Saturday there was “absolutely no evidence” a cyberattack caused the global IT failurer.

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

BA has not said what is causing the computer problem, but says it is working to resolve it as quickly as possible.

The Associated Press contributed to this report.