According to Sweden's public broadcaster SVT, the perpetrator entered the school wielding a sword, just after lunch, with police receiving the first calls at 2.06pm.

"We have an ongoing operation in the area and that is all we can say at the moment," says Pelle Vamstad, press officer at the police in Fagersta.

Several schools in the area have been evacuated as a result of the attack, and there are ambulances, police and police helicopters on the scene.

"We have been informed of a serious incident in Fagersta. The police are on site and are working very intensively on the incident. The government is in close contact with the police and is continuously monitoring developments," Sweden's justice minister, Gunnar Strömmer, told SVT.