Denmark’s Aalborg airport has been shut due to drones in its airspace.
Northern Jutland police told reporters “more than one drone” had been sighted near the airport and they were flying with lights on.
The drones were first seen at about 9.44pm (8.44pm BST) on Wednesday, according to police, and remained in the airspace until 12.54am on Thursday.
Eurocontrol, which oversees European air traffic control, had earlier said arrivals and departures at Aalborg airport would be at a "zero rate" until 5am BST on Thursday due to drone activity in the vicinity.
The drone sightings come two days after the country's main Copenhagen airport was shut for four hours over a similar incident that raised European security concerns.
"It is too early to say what the goal of the drones is and who is the actor behind," a police official said.
Northern Jutland police later said that efforts to take down the drones had been unsuccessful and the drone operators had yet to be apprehended.
Southern Jutland police said in a post on X that drones had also been observed near the airports in the Danish towns of Esbjerg, Sonderborg and Skrydstrup.
Fighter Wing Skrydstrup in Southern Jutland is the base for Denmark's F-16 and F-35 fighter jets.
Denmark said on Tuesday the incident at Copenhagen airport was the most serious attack yet on its critical infrastructure and linked it to a series of suspected Russian drone incursions and other disruptions across Europe.
The closure of Aalborg airport also affected Denmark's armed forces because it is used as a military base, police added. The Danish armed forces said they were assisting local and national police with the investigation, but declined to comment further.
Authorities in Norway also shut the airspace at Oslo airport for three hours on Monday evening after a drone was seen.
European Commission President Ursula von der Leyen said on Tuesday that the drones that halted flights at Copenhagen airport were part of a "pattern of persistent contestation at our borders."
Suspicions of Russian involvement in the Copenhagen airport incident were ungrounded, Russia’s ambassador to Denmark said on Tuesday.
Norwegian and Danish authorities are in close contact over the Copenhagen and Oslo incidents on Monday but their investigation has not yet established a connection, Norway's foreign minister said on Wednesday.
