The incident occurred on Friday afternoon at the Brinell secondary school, which has about 450 students aged 16 to 20, in Fagersta, a town of 13,000 inhabitants in central Sweden.
"We received an alarm at 2.06pm about suspected deadly violence and sent all available resources to the school," a police spokesperson told Reuters.
The spokesperson said one person at the scene was later taken into custody and that there was no longer any danger to the public.
The school had just opened after the northern hemisphere summer recess and for some students it marked the first day at the senior high school.
Several other schools and public buildings in Fagersta were also placed in lockdown after the sword attack took place.
Citing unnamed sources, the daily Expressen said police had shot the suspect in the case but Reuters could not immediately confirm the report.
The incident comes a year after a school shooting in Orebro, also in central Sweden, when a gunman killed 10 people before turning the weapon on himself, in the worst mass shooting in Swedish history.
The Swedish government is in close contact with the police following Friday's attack, Justice Minister Gunnar Strommer said in a statement to Reuters.
Swedish Prime Minister Ulf Kristersson said police were working intensively on the case and asked everyone to let them and the emergency services work undisturbed.
"Our thoughts are with all those affected," he wrote in a post on social media X.
Social Democrat leader Magdalena Andersson, whose centre-left coalition holds a clear lead in opinion polls ahead of next month's parliamentary election, said that "all of Sweden stands together with Fagersta at this difficult time".
with AP
11°C