(Adds total number held in custody)

COPENHAGEN, Feb 16 (Reuters) - Gangs of rioters set fire to cars and garbage trucks in northern Copenhagen on Friday, the sixth night of rioting and vandalism that has spread from the capital to other Danish cities, police said on Saturday.

Five youths were arrested in the capital on Friday after 28 cars and 35 garbage trucks were burned, Copenhagen police duty officer Jakob Kristensen told Reuters.

Danish media said arrests in other towns brought to 29 the number of people police were holding.

Scores of cars and several schools have been vandalised or burned in the past week. Police could give no reason, but said that unusually mild weather and the closure of schools for a winter break might have contributed.

Police arrested two Tunisians and a Dane of Moroccan descent on Tuesday for planning to kill a cartoonist who drew one of the cartoons printed in a Danish newspaper two years ago that roused a storm of protest in Muslim countries.

Fifteen Danish newspapers reprinted his drawing on Wednesday in protest against the alleged murder plot.

Several hundred Muslims gathered in central Copenhagen on Friday to protest against publication of the cartoon. Most Muslims consider depictions of the founder of Islam offensive.

Social workers said the arrests, the reprinting of the cartoon and protests against its appearance might have fuelled the riots.

Publication of the cartoons two years ago led to protests and rioting in Muslim countries in which at least 50 people were killed and three Danish embassies attacked. In October police arrested more than 400 people in Copenhagen after demonstrators evicted from a youth centre earlier in the year tried to occupy a new building. (Reporting by Kim McLaughlin, editing by Tim Pearce)