Copenhagen Airport, the busiest in the Nordic region, has reopened after drone sightings halted all take-offs and landings for nearly four hours, while Norway's Oslo Airport shut its airspace over a drone.

"The police have launched an intensive investigation to determine what kind of drones these are," Copenhagen Police Deputy Assistant Commissioner Jakob Hansen told reporters.

"The drones have disappeared and we have not taken any of them," he added.

Hansen said authorities in Denmark and Norway would co-operate to determine whether there was a link between the two incidents.

Oslo Airport shut its airspace due to a drone observation, a spokesperson for Norwegian airport operator Avinor said in an emailed statement, adding that all flights were diverted to the nearest airport.

Danish

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