The incident occurred on Saturday evening and according to P4 Västmanland, the police have cordoned off a large area in Skallberget in Västerås.
Three people are said to have been shot and taken to hospital, but the extent of the injuries is still unclear, reports Aftonbladet.
The police write on their website that a “serious crime” has occurred, but do not confirm that it is a shooting.
According to a witness on the spot, police technicians and dog patrols are working to try to secure traces such as blood and empty shell casings along, among other things, footpaths.
The text is updated.