The attack on Tuesday - described by Sweden's prime minister as the "worst mass shooting" in the country's history - happened at a school for adults.

Around 10 people were killed in a school shooting in Örebro. The damage at the crime scene was so extensive that investigators were unable to be more definitive, said Roberto Eid Forest, head of the local police.

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.

Police said they do not know the motive but do not believe it is terrorism, adding they "had no warning sign" about the attack. Officers are working to identify the perpetrator and the victims.

Swedish police found three rifles in the adult education centre in Orebro where a gunman killed 11 people and wounded several others this week in the country's deadliest mass shooting, a spokesperson said on Thursday.