A “technical issue” has hit UK air traffic control systems, with airlines warning of delays to flights.
Britain’s National Air Traffic Services said it was experiencing “technical issues” and has “applied traffic flow restrictions to maintain safety”.
“Engineers are working to find and the fix the fault. We apologise for any inconvenience this may cause.”
They did not provide any further information about what caused it or how long it would take to fix.
Scottish airline Loganair and EasyJet have both warned passengers there could be delays to flights.
Broadcaster Gabby Logan also said on X she was on a plane on a runway at Budapest airport, and had “just been told UK airspace is shut”, adding “we could be here for 12 hours”.
She said air traffic that was already airborne was being allowed to land, but nothing else was taking off.
Travel journalist Simon Calder said aircraft are coming down slowly, but that the “flow rate” – at which aircraft can land – has been significantly reduced.
He told BBC News that today is one of the busiest days of the year, as many people return from long weekend trips abroad – and the UK’s London Gatwick Airport is the busiest single runway airport in the world.
There is “no certainty about when it is going to be fixed” he said, adding that officials appear to “not know at this stage what caused the problem nor indeed how to fix it”.
“I fear there are going to be an awful lot of people waking up tomorrow where they don’t want to be,” he said.
Scottish airline Loganair said on social media site X, formerly Twitter, there had been a network-wide failure of UK air traffic control computer systems, warning some flights may face delays.
Emmet Lyons, a journalist for BBC’s US partner CBS News, said he had received an update from EasyJet while sitting on a plane on the tarmac in Spain.
The airline said it the air traffic control issue was “currently affecting all flights due to fly into or out of United Kingdom airspace”.
“We are working with the relevant authorities to understand the impact of this issue and the timescale for normal operations to resume,” it said.