The alarm about the explosion was reported to the police shortly after 3 am, on Sunday morning.
There are limited damages that this explosive charge has caused to the gate, but there are windows that have been blown out and it has been heard from a great distance, says the police's press spokesperson Ola Österling.
The explosion was powerful enough to trigger a burglary alarm at another address.
It's some kind of bomb. We do not believe it's a hand grenade, says Österling.
Three people were taken to hospital with shock injuries. No one was injured by the explosion itself, according to the police.
Bomb experts have worked on the site, the police have gone door-to-door in the area and used a dog. They have also stopped and checked several vehicles and questioned "a large number" of people, but no one has been arrested.
A preliminary investigation has been initiated for general endangerment and violations of the law on flammable and explosive goods.
