No one was injured, but a number of windows were broken.
The bomb squad will go there and see what this could be, then we will also do a technical investigation, said police spokesperson Carina Skagerlind.
A preliminary investigation into public danger and a serious violation of the Act on Flammable and Explosive Goods has been initiated.
The area is cordoned off, and police have checked people nearby. There are no suspects in the case.
