It is unclear what exploded, but it happened at a gate in an apartment building, according to police.
"A person has been seen running from the scene," police spokesperson Anna Lärk tells TT.
No one was injured, but the gate was damaged.
The case is classified as "destruction endangering the public" and a violation of the Act on Flammable and Explosive Objects. No one has been arrested. The National Bomb Squad has been called.
