The explosion occurred at 22.22 and caused damage to the door and windows of an apartment building.
No one was injured.
Even though there were no major damages, it's always serious when something explodes and this happened early in the evening, says Sebastian Börjesson, duty officer at Police Region West.
The police cordoned off large parts of the square during the night and the national bomb squad was called to the scene to ensure that no further detonations could occur.
We're piecing together right now who was the intended target and why, and if that person is in the stairwell, or if there's a company nearby that could have been the target, says Sebastian Börjesson.
At present, no one has been arrested and the area is considered safe now.
The incident is being investigated as reckless endangerment.
