Three people involved in a “serious crime” in a Swedish-registered car are being hunted by Danish police, according to a statement.
It says the three people are riding in a black Volvo V90, registration ZBP 546, and should not be approached.
“Witnesses who see the vehicle should contact the police immediately,” the statement said.
Swedish newspaper Aftonbladet reports there has been a kidnapping, although police have not given further details.
Authorities closed off transport links to and from Denmark’s largest island Zealand in their search. All of these links are now open or being reopened, police said.
The Great Belt Bridge, to the island of Funen, was wholly closed to cars, while ferries and trains were also affected.
Police armed with machine guns reportedly stopped a car on a motorway west of the capital Copenhagen (which is located on Zealand), according to a photographer quoted in newspaper Berlingske Tidende.
Dog patrols and a police helicopter are also reportedly near the scene.
“I was in the Danish police for 41 years and I have never experienced this sort of operation,” former head of Danish intelligence Hans Jorgen Bonnichsen reportedly told Danish tabloid BT.
Broadcaster TV2, however, says the police do not anticipate the operation will last long.
Traffic information account TrafikNyt says the Great Belt Bridge and the Oresund Bridge, which links Sweden to Denmark, have been reopened, and all ferries to and from Germany have resumed.
Copenhagen Police meanwhile have tweeted that Copenhagen railway station will reopen, and have said the Elsinore-Helsingborg ferry link to Sweden is now open again.