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.

The king and queen visited the scene of the tragic event that occurred on Tuesday and Swedish flags were flown at half-mast to honor the victims.

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.