Sweden: Dozens of cars set on fire in one night

It is not unusual for such attacks to take place in Sweden in the week before schools reopen after the summer holiday, Lippens told CNN, but "the current count and level of damage is unprecedented."

"The police have never seen this amount of vandalism and criminality before at this particular time," he said, referring to Monday's events in Gothenburg.

A smaller number of cars were also burned or vandalized in the capital Stockholm, the nearby city of Uppsala and the town of Falkenberg, close to Gothenburg, according to Swedish media.

The attacks mostly took place inside so-called high-risk areas that are characterized by high unemployment and low school attendance, Lippens said. Of the 23 high-risk areas identified by police in Sweden, seven are in Gothenburg.

Prime Minister Stefan Lofven said in an interview on Swedish radio Tuesday that the violence "seems very organized, almost like a military operation," Reuters reported. Crime and unemployment are key issues in Sweden ahead of the federal election in September.

Eyewitness Cecilia Sundborg told CNN she was at a friend's house in Gothenburg's southern Frölunda neighborhood -- where she also lives and which is listed as high-risk -- when she saw about eight to 10 masked people in a parking lot smashing car windows with baseball bats.

"They were very organized," she said. "A couple of them ran around pouring petrol on top of the cars. They had a grocery cart filled with what looked like Molotov cocktails. They were thrown into the back windows of the cars."

Sundborg filmed the burning vehicles from inside a building where she had sought refuge.

The attackers then fled the scene, leaving around nine cars on fire and another 10 to 15 otherwise vandalized, Sundborg said.

"People were crying and it was very tense everywhere," she said. "I was really scared but I was even more pissed off."