British Airways passengers have reported delayed and cancelled flights due to IT issues with the company's check-in systems this morning.
Images posted on social media showed long queues of holidaymakers on Wednesday morning as well as error messages with the BA app.
A BA spokesman said: "We are experiencing some systems problems this morning which are affecting check-in and flight departures.
"Please check ba.com and manage my booking for the latest flight information, and allow extra time at the airport."
The airline is using back-up and manual systems to try and cope with the issues.
BA said the systems issue had resulted in delays and cancellations from London airports.
It is offering short-haul passengers departing from Heathrow, Gatwick and London City the chance to re-book to another day between Thursday and next Tuesday.
A spokesman said: "We are working as quickly as possible to resolve a systems issue which has resulted in some short-haul cancellations and delays from London airports.
"A number of flights continue to operate but we are advising customers to check ba.com for the latest flight information before coming to the airport."