Rioting youths set fire to cars and trash bins and hurled rocks at police overnight as a spate of vandalism continued in Copenhagen and other Danish cities. Nine youths were arrested in the capital after a fifth consecutive night of unrest, mostly in immigrant neighborhoods. Six of them would 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 last weekend. 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."