People travelling by rail and plane have been affected by global IT outages.
Disruption has been reported on rail lines operated by Thameslink and London Northwestern while airline passengers have also reported problems at London Luton Airport.
Luton-based airline EasyJet said airports around Europe had been hit by the outage but the “disruption is not isolated to EasyJet” and described it as “extraordinary circumstance outside of our control”.
London Luton said it had appointed additional staff and was continuing to operate using manual systems where needed.
In a statement the airport said: “We are aware of an ongoing global IT issue that is impacting check-in and boarding procedures for some airlines.
“We have additional staff on hand to support, and operations are continuing with manual systems. Passengers are advised to check with their airlines for flight updates.”
Thameslink warned on social media that rail services for London, Bedfordshire and Buckinghamshire had been affected by “widespread IT Issues”.
London Northwestern, which runs services through the same counties, apologised on social media for any inconvenience caused.
Greater Anglia has warned some stations it serves have also been affected.
The firm runs trains between London Liverpool Street and London Stansted Airport, passing through Bishop’s Stortford, Sawbridgeworth and Cheshunt in east Hertfordshire.
Great Northern said LNER services between King’s Cross, Stevenage and Peterborough are also disrupted.