Denmark’s eastern island of Zealand, where Copenhagen sits, has been cut off due to “a major police operation”, authorities say.
Bridges from Zealand to the central island of Funen and to Sweden have been closed, and ferry crossings to Germany and Sweden have been cancelled.
A police helicopter and dog squads were spotted on a highway near Roskilde, 40 miles west of the capital Copenhagen, according to Denmark’s TV2.
Police issued an appeal for sightings of a black Swedish-registered Volvo car, saying there were likely to be three people inside involved in serious crime.
The people inside the car should not be approached, police added in a statement.
Sweden’s Aftonbladet newspaper quoted an unnamed police source as saying the car was being sought in connection with a kidnapping.