Thirteen people aged between 18 and 25 have been arrested after protesters set fire to two schools in the fifth consecutive night of riots in Stockholm.

Fifteen cars were torched on Thursday night across the Swedish capital's suburban neighbourhoods, and an attempt to set ablaze a police station was promptly quenched. Fire-fighters responded to some 70 emergency calls overnight.

"This makes me extra angry. Are things going to get better if people set schools on fire?" Aleks Sakala, a resident of Stockholm's northern district of Kista, asked the Expressen newspaper.

"This is as far from good sense as you can get. This is madness. Where will my kids go to school tomorrow? They probably won't be able to finish out the term."

Security reinforcements are converging in Stockholm from around the country to curb the spiralling street violence, which erupted days after a 69-year-old machete-wielding man was shot dead by police.

However police spokesman Kjell Lindgren said the fifth night of violence was less intense than the previous four, and the participants seemed less aggressive.

However riots now threaten to spread to other areas of the Scandinavian country, as episodes of vandalism have been reported in several other cities including Malmo, Boras and Karlskrona, Swedish daily Dagens Nyheter reported.

In Sodertalje, a town a few kilometres south of Stockholm, rioters reportedly threw stones at police responding to reports of car burnings.

Youths and migrants took to the streets to demonstrate against authorities' heavy-handed tactics and underlying racial discrimination, after officers gunned down an immigrant who had locked himself in his flat with a woman in Stockholm's north-western suburb of Husby.

Home to some 12,000 people, 85% of whom are not of Swedish origin, Husby has become the centre of the protests, with rioters throwing stones and bricks at security forces.

Sweden's world-famous welfare system is facing a youth unemployment rate of 25%, compared with the overall level of about 8%.

The unemployment rate among the immigrant community currently stands at 16%, ten points higher than that suffered by native Swedes.