The injured have been taken to Örebro University Hospital. All were awake and able to speak, according to Sören Gustavsson, team leader at SOS Alarm.
The motorcycle rally on Saturday was a major event in Svartå in Närke, near the border with Värmland, attracting many people.
It was a motor event where 200 to 300 people had gathered, says Anders Dahlman, press spokesperson for the police in the Bergslagen region.
The event came to an abrupt end when an explosion, possibly in an engine, occurred, according to police.
A representative for the organizer, the Swedish Transport History Society, told SVT that the accident occurred when a Rolls-Royce engine was being demonstrated. Parts of the engine are said to have been scattered about ten meters from the scene of the accident.
The alarm was raised at 11am and a major rescue operation was launched, including several ambulances and ambulance helicopters. The rescue operation ended shortly after lunch.
The police have launched a preliminary investigation into what happened, as the explosion created danger and caused bodily harm.
