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.

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".

Swedish police said they were still investigating the motive behind the country's deadliest mass shooting, as local media began reporting details about the gunman. The suspect, named in reports as 35-year-old local man Rickard Andersson,