A gunman opened fire at an adult education center in the Swedish city of Örebro on Tuesday, killing at least 10 people in what the country’s prime minister called the “worst mass shooting in Swedish history.

Witnesses who survived Sweden’s worst mass shooting have described horror and panic that gripped an adult education center west of Stockholm as the gunman killed at least 10 people.

As many as 10 people have died in a shooting at a school in Sweden, police have confirmed. The deadly attack happened on Tuesday afternoon at Risbergska School, an adult education centre, in the city of Örebro, about 125 miles west of Stockholm.