The alarm about the explosion came at 8:30 p.m. on Tuesday, according to the police.
"We are receiving an alarm about an explosion in or next to an apartment stairwell. There are no reports of injuries," says Jakob Palmgren, police press spokesman.
The police have set up cordons in the area around the property. The National Bomb Squad is on its way to the scene. The residents of the building have been evacuated from their apartments.
There was some smoke in the stairwell after the explosion, but there appears to be no fire in the building.
The incident is being investigated as a public nuisance.
