“A suspect has been arrested and taken to hospital. I do not know the extent of his injuries,” said police spokeswoman Towe Hägg.
The fire broke out at around 4.30pm at the ground-floor flat in Lappkärrsberget on the university campus. A number of student residences are situated in the area.
Fire crews took 30 minutes to extinguish the fire, by which time the interior of the apartment had been largely destroyed.
Some 15 people were evacuated from the building. A number of residents had gathered in a nearby building. Students living in other apartments in the block were told after 6pm that they would not be allowed to return overnight. Social services have been informed that around 50 people need shelter.
The suspect has been taken to Danderyd hospital. It is so far unclear why he is suspected of a crime.
Police said they plan to question witnesses and carry out a forensic examination of the scene.