Three people involved in a "serious crime" and travelling in a Swedish-registered car are being hunted by Danish police.
A statement says the three 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 briefly closed off transport links to and from Denmark's largest island Zealand in their search, but later reopened them.
The Great Belt Bridge, to the island of Funen, was wholly closed to cars, while ferries and trains were also affected.
A later tweet from the Copenhagen police apologised for shutting down transport, and said there was nothing new to report on the case.
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 were 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 told Danish tabloid BT.
Traffic information account TrafikNyt said the Great Belt Bridge and the Oresund Bridge, which links Sweden to Denmark, were reopened at around 16:00 local time (14:00 GMT), along with all other routes to and from the island - including ferries, which also suffered disruption.