Most flights from airports in the United Kingdom were suspended Thursday after a massive air traffic control systems (search) failure, the British Broadcasting Corporation reported.

All flights from London's Heathrow Airport (search) were suspended, a Reuters reporter said. The BBC reported that the computer systems at the Manchester and Bristol airports were operational again.

The cause of the failure was not immediately known. The U.K.'s National Air Traffic Services (search) said flights have been grounded so any planes still in the air can be prioritized, and that delays should be expected throughout the day, the BBC reported.