Police were working on the theory that some kind of homemade bomb caused the blast at the Cybergymnasiet school near Järntorget square at lunchtime. One student was arrested on suspicion of devastation endangering the public and police began interviewing him in the afternoon.
Bomb squad officers were called to the school to investigate after it was evacuated, before a forensic investigation later got underway. No one was injured, and the explosion did not cause any major damage.
Newspaper Göteborgs Posten reported that the blast was heard coming from a toilet in the school, but police did not want to reveal exactly where it occurred.
“It is not in the area where lessons take place in any case,” police spokesperson Stefan Gustafsson told news agency TT.
There are no known threats against the school or anyone who attends it, police said. Workers in the area were allowed to return to their workplaces by Wednesday evening.