Flights in and out of Belgian airports have been disrupted due to a technical glitch at the domestic air traffic controller, Belgocontrol.
Belgocontrol said the chaos was caused by a power surge, which knocked out emergency generators.
Passengers faced delays at Brussels, Antwerp, Liege and Charleroi.
Belgian airspace remained open to those aircraft flying over the country at high altitudes.
Budget airline Ryanair reported delays and diversions.