Thousands of passengers had their flights delayed or canceled at the world's busiest airport Wednesday after a baggage system computer crashed.

The problem at Heathrow Airport began Tuesday at Terminal 4 when the automatic baggage sorting system's computer went down while being upgraded.

BAA PLC, which owns Heathrow and the faulty system, said the crash prevented workers from being able to place luggage into the area where it is sorted for flights.

The biggest victims were British Airways passengers on long-haul flights. Many were left waiting outside the terminal to find out if their flights would be canceled.

British Airways is the main carrier at Terminal 4, which handles domestic and international flights. Other smaller carriers managed to handle luggage by hand and keep their flights going.

The problem occurred one day after a European airline group reported that Heathrow, the world's busiest airport, had suffered more delays than any other major European airport for the second straight year last year.

About 35 percent of flights at Heathrow were delayed last year, the Association of European Airlines said. Heathrow handles more than 480,000 flights a year, and it is Europe's main hub for flights to the rest of the world.

BAA apologized Wednesday to British Airways passengers whose travel plans were disrupted and said the computer problem would be fixed by Thursday. It also urged all passengers to check with their airlines before traveling to Heathrow for flights.