It was "absolute chaos," passenger Barry Goldstone told The Daily Telegraph in a story published Monday.
Goldstone, who was trying to fly from Britain to Denver, was one of many in Terminal 5 unable to check their luggage because of a mechanical failure.
"They don't seem to have any continuity plan if anything goes wrong, and unfortunately they don't seem to have any consistency of information either," Goldstone said of airport officials.
After several hours, airport officials suspended baggage check-in, letting only passengers with carry-on luggage board the planes owned by British Airways, which has sole use of Terminal 5.
The check-in problem was fixed by late afternoon, but by then many people had missed flights and were forced to rebook for Monday, the Telegraph reported.