CNN) -- Police in the Swedish capital, Stockholm, have called in reinforcements after the city's suburbs were hit by a fifth night of riots.

Gangs set fire to two schools and a police station in the city on Thursday, police spokesman Kjell Lindgren told CNN.

About 30 cars were also torched, with the blaze from one vehicle spreading to a nearby shop.

"Police and firemen were also attacked again with rocks overnight, but no one was severely hurt," Lindgren said. "The level of violence has decreased," he added, "but the problem remains."
Third night of riots hits Sweden

Extra police have been called in to help officers deal with the riots and a number of other events, including football matches, planned to take place in the city over the weekend.

Read more: Swedish suburbs shaken by violence

"Our resources are very stretched, so we need additional officers to make sure we cope with all the events and this violence," Lindgren said.

The riots broke out after days of rising tensions following the death of a 69-year-old man who was shot by police earlier this month while wielding a machete in the Stockholm suburb of Husby.

However, police say they are not sure what sparked the outbreak of violence.

The area is blighted by high unemployment and crime levels.

A total of 29 people have so far been arrested in connection with the riots, Stockholm Police said in a statement on their website.

Read more: Swedish capital sees 3 nights of riots

The city's police chief pledged that more culprits would likely be arrested in the coming days.

"Initially we encountered a lot of violence, so our priority was to ensure the safety of the firemen," Mats Lofving said in a statement. "Now we are gearing up our ambition to start arresting more people.

"We have a lot of filmed material that we will be studying closely. We hope to arrest more of those who may think that they have gotten away with it because the worst is over."

Earlier this week, Swedish Prime Minister Fredrik Reinfeldt vowed to take a stand against the rioters.

"We have to show that we won't allow a group of young men who believe in the use of violence to run society," Reinfeldt said.