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".

The police responding to the attack encountered firing so intense that they struggled to tell how many gunmen were on the scene, an official said.

The mass shooting in Orebro occurred in spite of Sweden's strict gun laws. Though gang violence has been increasing in Sweden, Fox describes the tragedy as an outlier while noting Sweden's rate of 0.3 firearm-related homicides per 100,000 population.