The apartment block in the Rinkeby suburb of Stockholm was evacuated on Friday morning while firefighters tackled the blaze.
"The entire attic is pretty much in flames, so we're going to let it burn off," emergency control room officer Ulf Larsson told the TT newswire on Friday morning.
There were initial fears the fire could spread to a preschool connected to the building. However by 10am firefighters said they believed they were slowly starting to get the blaze under control.
"The risk it could spread is not completely gone, but things are looking better," said control room officer Jonas Fröjmark.
Firefighters preventing the fire from spreading. Photo: Pontus Lundahl/TT
Emergency services were first called to the scene at 4.54am and by 10am 14 fire engines were busy fighting the flames. Police have launched an investigation into aggravated arson.
No casualties have been reported.