Rioting youths set fire to cars and trash bins and hurled rocks at police overnight Thursday, as a spate of vandalism continued in Copenhagen and other Danish cities.

Muslim men protesting Danish newspapers' re-publication of a cartoon of the Prophet Muhammad in Copenhagen Friday.
(John McConnico/Associated Press)

Nine youths were arrested in the capital after a fifth consecutive night of unrest, mostly in immigrant neighborhoods. Six of them will likely be charged with violence for throwing rocks at police officers, Copenhagen police operations chief Per Larsen said Friday. There were no reports of injuries.

Police said they were not sure what triggered the unrest. Some observers said immigrant youths were protesting against perceived police harassment and suggested the reprinting of a cartoon of the Prophet Muhammad in Danish newspapers Wednesday may have aggravated the situation.

"It has been a very busy night for the police and the firefighters here," said Henrik Andreasen, a spokesman for police in the western suburbs of Copenhagen. "It has been a bit insane."

Firefighters responded to dozens of fires in and around the capital. About 10 cars were torched in Kokkedal, north of Copenhagen, while a school in Bagsvaerd, west of the city, was partly destroyed in a presumed arson attack, police said.

In some cases, firefighters said they were hindered from putting out the fires by rock-throwing youths.

There were also reports of fires and vandalism in other Danish cities, including Aarhus, Ringsted and Slagelse. No arrests were made in those cities.