The National Bomb Squad has arrived at the scene, police announced shortly after 9 p.m. on Tuesday.
In addition to the bang, which according to the police came "from a public area inside the property," the stairwell was also filled with smoke.
The police write on their website that there are no reports of personal injuries. However, there is said to have been material damage to "a window and a gate."
At 9:20 p.m., the police announced that the preliminary investigation has classified the crime as public destruction and a violation of the Act on Flammable and Explosive Goods.
The alarm about the explosion came at 6:10 p.m.
