Students and teachers recalled trying to save the lives of their comrades before fleeing the scene of a mass shooting in Sweden described by the prime minister on Wednesday as a "dark day" in the country's history.

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."

Survivors of Sweden's worst mass shooting on Wednesday recalled trying to save the lives of their comrades at a school for adults in Örebro, a day after a gunman killed 11 people on what the prime minister called a "dark day" in the country's history.