Masked youth torched dozens of cars overnight in Sweden and threw rocks at police, prompting an angry response from the prime minister, who on Tuesday spoke of an "extremely organized" night of vandalism.

Police spokesman Hans Lippens said Tuesday that initial reports indicate that about 80 cars were set ablaze overnight, chiefly in Sweden's second largest city, Goteborg, and nearby Trollhattan, an industrial city.

Fires were also reported on a smaller scale in Malmo, Sweden's third largest city.

In Trollhattan, northeast of Goteborg, where at least six cars were burned, rocks were also thrown at police and roads were blocked. Goteborg is 400 kilometers (250 miles) southwest of Stockholm.

Lippens added that because the fires started within a short period of time, "we cannot exclude that there is a connection between the blazes."

Photos posted by Swedish tabloid Aftonbladet showed black-clad men torching cars on a parking lot outside a Goteborg suburb.

Sweden's news agency TT said witnesses had seen "masked youngsters" running away. No arrests have been made.

Swedish Prime Minister Stefan Lofven lashed out at the perpetrators, asking them "what the heck are you doing?"

In an interview on Swedish radio, he said he was "really getting mad" and that "the society must react in a tough manner." He said the fires seemed to be "extremely organized."

No injuries have been reported. However, the fires tie up police and rescue officials and frighten residents.

"You damage residential areas and ruin it for your neighbors," Lofven said.