Passengers travelling from Heathrow Terminal 5 are being warned of delays following a fault with a baggage check-in system yesterday.
The airport says they should check the status of their flight with their airline.
British Airways said a small number of passengers missed flights from T5 yesterday morning as they were unable to check in bags.
Other passengers who were unable to check-in their luggage travelled without their bags. It said: "We are sorry for any inconvenience to customers and we are working hard with the airport owner to minimise any disruption.
"All of our flights continue to operate as normal but some have departed with a number of bags missing.
"We are doing all we can to reunite customers with delayed bags as quickly as possible.
The BBC said there was a queue of about 500 people waiting to rebook flights yesterday lunchtime.
An airport spokesperson said the problem in Terminal 5 had been resolved, but passengers were facing long queues and delays.
The airport told the BBC: "Our teams have now restored all check-in services and we have additional staff in the terminal to help passengers."
The airport said passengers who wished to take hand luggage on board were unaffected.
It said the problems started at around 09:00 and were resolved by 11:30.
