Four of the victims were seriously injured, according to the Wiadomosci newspaper.
The Norwegian driver was detained by Polish police following the incident, with the racing event organizers set to give a press conference on Monday.
Reporting from the scene by the TVN news network
"The drivers started off too quickly, and the driver didn't have any control over the vehicle," reported the Polish television network TVN24.
The yellow car was seen swerving across the tarmac, skidding dangerously close to the barricades at several turns, before the side of the vehicle finally rammed into a tight cluster of racing enthusiasts. The impact saw the victims fly across the pavement.
Images from the aftermath show the injured strewn against a grass bank, with contorted metal barricades visible in the frame, as fellow bystanders rushed to their aid.