In a video shown on tabloid Aftonbladet's website, a grey car is seen speeding across the Medborgarplatsen square in Stockholm's Södermalm district and smashing into a group of young people wearing white student caps.

The incident took place outside a popular outdoor drinking spot shortly after 6 p.m. on Walpurgis night, according to Sveriges Radio.

Four people were brought to hospital. The police told Aftonbladet that there must have been "something wrong with the car".

"It is unfortunate when people get injured by a police car that is not going to stop," Towe Hägg, information officer at the Stockholm police, said.

Police received an alarm of a large disturbance at the square shortly after 6 p.m. A large number of students had gathered at the square where between 10 and 100 people were reportedly involved in a fight. According to a number of witnesses, the unmarked police car drove straight into the crowd, a fact supported by video recordings. The police told Aftonbladet that the driver had stated that it was not possible to bring the car to a halt.

The speeding police car has been impounded and the incident will now be investigated by the unit for internal investigations. A prosecutor has been informed of the case, too.

On Friday, two out of four injured remained in hospital for observation, with medical staff suspecting they may have suffered concussions.