Emergency services were called out to the blaze in the Råslätt area of Jönköping shortly after 2am.
Two people jumped from the building to escape the flames. One of them was caught by a life net and escaped without serious injuries, but the other person jumped before fire services arrived and was seriously injured. Swedish media reported they had jumped from balconies on the seventh floor, which is the top floor.
The county hospital in Ryhov confirmed that one person was “critically injured”, another two people suffered medium injuries and were being treated in hospital.
The other eight were understood to have minor injuries, mainly due to smoke inhalation.
Around 200 residents were initially told to evacuate the building, although the fire mainly affected the apartments of around 50 people. Most people were able to return later on Thursday morning, according to the housing firm Vätterhem.
Most of the people who live in the building are students, and the fire is believed to have started in a student apartment. Police have opened an investigation into “carelessness endangering the public”.
The blaze was extinguished by 3am and the area has now been cordoned off while police and fire services investigate the cause of the fire.