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.

Police in Sweden said "about 10" people were killed in a shooting at an adult education school . The shooting occurred at Campus Risbergska in Örebro, Sweden, the city said in a statement. Police say the shooter is believed to have been killed.