Flights have been cancelled and delayed after a technical glitch in Switzerland's air traffic control system.

       It saw Swiss airspace closed on Wednesday morning, halting takeoffs and landings at airports in Zurich and Geneva airports for hours.

       Pan-European air traffic agency Eurocontrol warned airlines in a bulletin to expect "high delays".

       Geneva Airport said air traffic had gradually resumed since 8:30 CEST. Several flights had been cancelled, it said on Twitter, telling travellers to check with their airlines to see if their flight is still on.

       Zurich Airport said flights are running again.

       "Flight operations are planned at 50% capacity until 9:30 CEST and at 75% capacity from 9:30," the airport said in a statement.

       Zurich airport had scheduled 330 flights and Geneva 211 on Wednesday, according to FlightRadar24 data.

       Earlier, air traffic control agency Skyguide said it had closed Swiss airspace to ensure safety after a technical malfunction.