All British Airways flights from Heathrow and Gatwick have been cancelled for the remainder of Saturday, the airline has announced.
BA had earlier said no planes would take off from the two airports before 6.00pm but has now extended this.
It comes after a huge IT failure led to chaos and confusion at airports across the world, with 'wall to wall' queues reported at Heathrow's Terminal 5.
Passengers have been ordered to exit airport terminals without their baggage, with some travellers claiming they had been told it could take a week for them to be given their bags back.
Some travellers are stranded at airports around the world, with BA staff unable to rebook them on to other flights because the company's IT system remains down.
A spokeswoman for the airline said: "We have experienced a major IT system failure that is causing very severe disruption to our flight operations worldwide.
"We are extremely sorry for the inconvenience this is causing our customers and we are working to resolve the situation as quickly as possible."
"We've found no evidence that it's a cyber attack", the airline added.
