Austria came to a standstill on Wednesday to mourn victims of one of the worst outbreaks of violence in its modern history, as authorities search for clues to why a 21-year-old gunman shot dead 10 people at his former high school before killing himself.

Officials in Austria say a school shooting has left at least 10 people dead in the European nation's second-largest city, Graz. The shooter is also dead.

Students were sitting in their classrooms at a secondary school in Graz when a 21-year-old Austrian man shot dead nine people, before killing himself.Twelve people were injured in Tuesday morning's violence,