"There are five injured who have been transported to hospital. Two are reported to be lightly injured, and three seriously injured," Stockholm police said in a statement.
"The driver of the car is one of the injured."
The cause of the accident, which occurred at the Ticksta racetrack in Rimbo north of Stockholm, was not immediately known.
So-called "folk racing" is a form of rally popular in the Nordic countries, run with standard, inexpensive cars on special gravel or tarmac tracks of 2.4 kilometres (1.5 miles).
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