The detonation occurred sometime after 2 am. The police have launched a hunt for the perpetrators, but by 4 am, no one had been arrested.
No personal injuries have been reported.
I can't say more than that we've launched a hunt for the perpetrator or perpetrators, and they're suspected of general destruction and violating the law on hazardous and explosive materials, says Mats Eriksson, press spokesperson for the Stockholm police.
The explosion occurred on the sixth floor of the apartment building, but it's still unclear what exploded.
We don't think it's a hand grenade, but it's unclear for now. No one has been injured, but there's been some property damage, mainly some broken glass in the stairwell, so we've asked people not to leave their apartments because of it, says Mats Eriksson.
A large area has been cordoned off around the site, and the police are now trying to figure out who or what the explosion might have been intended for.
There's no danger now for the residents of the building or the area, says Mats Eriksson.
The rescue services initially had a large response on site, but began to scale back later. Technicians are expected to arrive at the site in the morning.
