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".

One day after the killings at an adult educational center, some gathered to lay flowers and come to grips with the violence.

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