Dozens of flights have been diverted away from Gatwick Airport and others face "heavy delays" or cancellations after an issue with air traffic control.
A number of restrictions have been put in place after a "short notice staff absence" was reported at the Sussex airport.
A spokesman for Gatwick Airport confirmed "22 flights have been cancelled" but said, "the situation is however improving with an additional air traffic controller now in place".
"The air traffic control restrictions are reducing as a consequence and more aircraft are able to arrive and depart," they said.
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Flights have been diverted to Heathrow, Luton, Bournemouth and Stanstead.
"Due to a short notice staff absence in the Air Traffic Control tower, temporary air traffic control restrictions have been put in place this afternoon," a spokesman for the airport said.
"This will cause some delays.
"Gatwick would like to apologise. Please contact your airline for more information."
Several unhappy travellers took to social media to vent their frustrations.
One passenger was on a flight from mainland Europe to Gatwick, when his flight was diverted to Brussels.
He said passengers were given no information and only found out by looking at the interactive flight map.
Another traveller took to social media to express their anger.
"Stuck on the tarmac in Bilbao being told that our @vueling flights can’t take off as there is only one person working in traffic control in Gatwick Airport - is this possible?
The National Air Traffic Services (Nats), which provides en-route air traffic control services to flights in the UK, has apologised for the issues.
In a statement, they said: "We are working closely with the airport to ensure we can handle flights with as little disruption as possible and we apologise very sincerely to people who have been inconvenienced as a result of unavoidable diversions.
"We are working closely with Gatwick Airport Ltd to build resilience in the airport’s control tower to ensure disruption is kept to a minimum. New air traffic controllers have been recruited since last summer, increasing our presence by 17 per cent, and others are due to start after completing their training, in line with the agreed plan when Nats took over the contract last October.
Passengers on flights that were diverted said they were given little to none information
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"London Gatwick’s senior management understands that we are working hard to keep the operation moving.
"Airlines operating at London Gatwick were aware of the situation when Nats was appointed but that does not dilute the apology we offer sincerely to them and their passengers who have been inconvenienced by recent disruption."
Last month, a technical issue at Nats led to 2,000 flights being cancelled.
Controllers were been forced to reduce the number of flights able to land and take off, which resulted in travel chaos.
One passenger who was stuck at Gatwick airport told GB News: "We've been told that the issues mean that our plane isn't due to leave for another seven hours.
"I was only going for a short break. To make matters worse, they've told us that things could change at any point so we shouldn't leave the gate in case they can suddenly take off sooner.
"It's complete chaos. My relaxing holiday is now ruined."
