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.

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."

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

The authorities said that at least 11 people were killed and that the suspect was believed to be among the dead.

Sweden's worst ever mass shooting this week has raised questions about the country's gun laws and widespread gun ownership.

Sweden’s worst mass shooting left at least 11 people dead, including the gunman, and at least five seriously wounded at an adult education center west of Stockholm. The gunman’s motive hadn’t been determined by early Wednesday as the Scandinavian nation — where gun violence at schools is very rare — reeled from an attack.