According to police, tenants in the four-storey building on Keplers gata in the Bergsjön district of Gothenburg were awakened by an explosion in a flat that was already on fire.
Screams could be heard from the apartment, as well as a smoke alarm.
“It sounded like a bomb. I opened the window and heard people screaming,” Medzide Cerimi, who lives across the street from the building but was nevertheless awakened by the blast, told the TT news agency.
The cellar of the building was also heavily damaged by the fire, which produced thick smoke.
Emergency services received a call about the blaze at 4.30am and by 7am the fire was completely extinguished.
“It was chaotic when we arrived. There had been some form of explosion,” Urban Samuelsson of Gothenburg emergency services told the Expressen newspaper.
According to emergency crews, no residents remain in the building and several have been taken to hospital.
A man and a woman from the flat where the fire is believed to have started have been taken to Sahlgrenska University Hospital where they are being treated for burn and smoke inhalation injuries.
The man, who is in his mid-30s, reportedly has burns over his entire body, with police adding that he remains sedated with serious injuries.
Another person has been taken to Östra Hospital with smoke inhalation injuries. Betweeen ten and 15 other residents were also taken to Sahlgrenska with smoke inhalation injuries.
Police have launched a preliminary arson investigation and the area has been cordoned off in anticipation of a forensic investigation.
The woman who was in the apartment where the fire began will likely be interviewed by police. She is in her early-30s and has mild smoke inhalation injuries.