Some 50 people were evacuated from the building. The injured man was brought to local Sahlgrenska Hospital where he is being treated for extensive burns and smoke inhalation. Police have launched a preliminary arson investigation.
The fire may have started in the cellar and spread into an apartment following an explosion.
"We think that the fire started in the cellar and that all of the oxygen was consumed in the blaze. When air entered the space when a door was opened or a window was broken, an explosion can have occured," police spokesperson Björ Blixter told Swedish Radio News.