British Airways has cancelled all flights scheduled to leave on Saturday from London's Heathrow and Gatwick airports, after the airline suffered a global IT systems meltdown.
Cancellations and delays could extend into Sunday, the airline said, although long-haul flights landing in London would likely be able to land.
In a statement British Airways said: "We are working to restore our services from tomorrow, although some delays and disruption may continue into Sunday."
The crash in the computer system used to keep track of passengers has left the airline unable to allow people to board flights. It also affected the airline's call centre and website, making bookings impossible.
The airline said there was no evidence the systems failure had been caused by a malicious hack, but said it is still investigating the causes.
The airline, which is owned by the Anglo-Spanish FTSE 100-listed International Consolidated Airlines Group, urged passengers on British Airways flights from Heathrow and Gatwick on Saturday not to come to the airport.
In an earlier statement British Airways said: “We have experienced a major IT system failure that is causing very severe disruption to our flight operations worldwide."
Passengers around the world are being forced to endure long delays. A British Airways pilot in Rome's Fiumicino airport said the problems meant none of the airline's planes could depart "from anywhere in the world", according to a video posted by a BBC reporter.
Passengers reported massive queues at Heathrow, with others saying on social media that their plane was stuck on the runway for more than an hour.
Meanwhile automatic check-in computers did not function correctly at Heathrow. Passengers were delayed at the airport, British Airways' central operations base, with Heathrow saying it has called in extra staff to help customers.
A spokesperson for the airport said: "Following an issue with a worldwide British Airways' IT system, British Airways have cancelled all of their scheduled departure flights from Heathrow, and Gatwick, this evening (UTC+1). All passengers booked onto these flights should not travel to the airport today."
Passengers travelling with British Airways tomorrow morning should check the status of their flight before travelling to the airport.
Flights from Heathrow to destinations around the world were delayed, according to the airport's website. British Airways flights to Berlin, Nice, Geneva, Madrid, Amsterdam and Glasgow were among those delayed or cancelled.