Two knife-wielding robbers entered a secondary school in Sweden on Monday and stole computers from students, local media has reported.

The masked men entered the classroom of the school in Vasteras as a lesson was taking place.

The men took all of the class’s computers but were forced to discard some after teachers chased after them.

No students or staff were injured but a passerby who tried to intervene was treated by paramedics on site.

Police did not provide full details of the robbery but said officers had been called to the scene after “multiple perpetrators” forced people to hand over electronic devices.

Tobias Ahlen, spokesman for the local police, said officers are patrolling the area.

School principal Henrik Pettersson said a number of the students did not feel well during the afternoon.

“There are many who are sad, upset and shocked to have witnessed such a horrible and traumatic event,” he told the newspaper Aftonbladet.

“This kind of thing should not happen in a school, it’s awful,” Mr Pettersson added.

Those in the class and the teachers who chased after the robbers are receiving support, the school said.