Police in Austria were hunting for clues on Wednesday after a gunman opened fire at his former high school a day earlier, killing nine students and a teacher in a deadly spree that stunned the country.

Austrian authorities were searching on Wednesday for clues to why a 21-year-old gunman shot dead 10 people in a rampage at his former high school before killing himself, in one of the worst outbreaks of violence in the country's modern history.

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.