British Airways flights were facing delays in and out of London's Heathrow and Gatwick airports on Thursday after a technical glitch overnight, the airline said.
"Our teams are working hard to resolve a technical issue which is affecting some of our flights," said a spokeswoman for BA, owned by airlines group IAG.
"We have rebooked customers on to alternative flights and offered hotel accommodation where they have been unable to continue their journeys last night.
"We are very sorry for the disruption to their travel plans. We plan to operate a full flight schedule today," she added.
BA warned that there would be knock-on delays -- but declined to comment on the nature of the problem nor the number of flights affected.
"This is the latest in a long line of British Airways technical glitches causing delays and cancellations," said Rory Boland, editor of consumer magazine Which? Travel.
"Yet again it's thousands of passengers who are paying the price -- left tired, frustrated and with a lack of information and assistance from the airline."
BA suffered a computer glitch in 2016 that severely affected its global check-in system.
Meanwhile only two months ago, the airline was forced to ground its entire UK fleet for two days when pilots went on strike in a bitter and long-running pay dispute.