STOCKHOLM (AP) — Swedish aviation officials say a solar storm has knocked out their air traffic control systems, prompting them to shut down the country's airspace for more than an hour.

The civil aviation authority said the solar storm Wednesday created disturbances in the Earth's magnetic field, which affected radar installations in southern Sweden. It wasn't immediately clear whether other countries also were affected.

Agency spokesman Per Froberg said flights disappeared from radar screens in Swedish air traffic control towers during the blackout, which lasted about an hour until 5:30 p.m. (1630 GMT). Froberg said it was unclear why the impact was so severe, adding the last time something similar happened in Sweden was in 1999.

He couldn't say how many flights were affected, but the country's main airports listed dozens of delays.