Officials in Sweden have vowed to determine why a man killed 10 people, and apparently himself, in an unprecedented attack that's shaken their "society to its core."

A gunman who killed 11 people, including himself, at an adult education centre in central Sweden may have been a student at the school, police said on Thursday, as they described chaotic scenes after the country's deadliest mass shooting as being like an "inferno".

Salim Iskef, 29, fled the Islamic State and Syria to form a better, more secure life in Sweden, only to be gunned down this week in the worst mass-shooting in Swedish history. Iskef was one of 10 people in the adult school in Orebro who were killed by the shooter,