British airports were still paralyzed on Thursday morning after a temporary computer failure at Britain's main air traffic control center was ended.

The National Air Traffic Services said the air traffic control system at Swanwick, southern England, which went down at about 6 a.m. (0060 GMT), was now fully operational, but most flights remained on hold.

"Safety being our primary concern we are now working to make sure those aircraft in the air and in need of landing should be able to do so to clear the delays," said Adrian Yalland, spokesmanfor the air traffic control center.

"The fault is thought to lie with the data processing system," Yalland said.

"The reason why planes were grounded was because we couldn't let them into the air which would add more complications," he said."We wanted to ensure the safety of flights in the air."

Yalland said he did not know how many flights had been affected by the computer crash or how long the delays would be.

Many airports are advising people to check in as normal, but delays are likely to continue throughout the day.