The driver, a man in his 25s, was already taken to hospital when the police arrived at the scene, but is not believed to have been conscious after the accident.
The accident occurred in an industrial area. The man collided with a trailer that was stationary and not attached at the time.
We do not really know what happened, but have been on the scene and heard people, says the police's press spokesperson Magnus Jansson Klarin.
The alarm came in to the police at 15.15 on Wednesday.
The police will conduct a technical examination of the motorcycle.
