London (CNN Business) British Airways canceled more than 100 flights Wednesday after the airline's computer systems crashed.

The cancellations hit thousands of travelers using London's Heathrow and Gatwick airports. Another 300 flights faced delays of up to an hour, according to the airline's website.

International Airlines Group ICAGY British Airways , which is owned by, said its check-in and flight start systems suffered a partial crash, and that it was using "backup manual systems to keep our flights operating."

A spokesperson for the airline said it would allow customers on canceled flights to rebook for between August 8 and August 13.

British Airways did not say what caused the computer outage. Later Wednesday, the airline apologized to customers and said the problem had been resolved.