Two people have been arrested on suspicion of arson in connection with the incident.
Due to the severe course of the fire and the fact that the neighbouring apartment was also affected, the case has been classified as arson, but the crime classification may change, Göran Håkansson, duty officer at police, tells TT.
The two people arrested were taken to hospital after suffering smoke inhalation. The extent of their injuries is unclear.
According to GP, a large rescue operation was dispatched, involving seven ambulances, rescue services and police.
The alarm came just before midnight and by 1:30 a.m. Saturday morning the fire was extinguished. A technical investigation will be conducted into what caused the fire.
