A wave of vandalism continued across Denmark for a seventh consecutive night, officials said Sunday.

Eleven people were arrested on suspicion of vandalizing and torching schools, cars and garbage containers, with 25 small fires burning overnight, police said.

The unrest, largely in immigrant neighbourhoods, has spread through Copenhagen and across Denmark.

Police are unsure what triggered the unrest, but some say youths from Denmark's immigrant communities were protesting perceived police harassment — anger apparently aggravated by the republication Wednesday of a cartoon lampooning the Prophet Muhammad.

Most of the unrest was reported in Copenhagen, particularly in the southwest, with four arrests and 14 fires in the capital alone, police spokesman Jan Marker said.

Part of a school in the Tingbjerg neighbourhood of Copenhagen was damaged by flames that tore through staff rooms and other administrative offices.

"But the general picture is that it looks calmer," Marker said. "It's not as bad as the previous night. It could be because of the arrests we've made."

On Wednesday, more than a dozen Danish newspapers reprinted a cartoon that had sparked protests in Muslim countries two years ago in a gesture of solidarity after police revealed an alleged plot to kill the cartoonist.