Swedish police said Thursday they met a scene resembling "an inferno" when they arrived at the scene of country's worst mass shooting that left 10 dead plus the gunman.

Regional police chief Lars Wiren said officers sent to the adult education centre in Orebro, west of Stockholm, told reporters they were faced with "dead people, injured people, screams and smoke".

Anna Bergkvist, who is heading the investigation, said they were still working to pin down a motive for Tuesday's massacre, which has sent shockwaves across the Nordic country.