Sweden is reeling from the country's deadliest mass shooting this week as investigators continue to look into the gunman's motive.

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

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."