A person in the Råby district of Västerås was taken to hospital by ambulance after being injured by a stabbing weapon in an apartment, the police report on their website.
The police are now investigating the incident as an attempted murder.
The person's injuries are described as serious, but according to the hospital, the condition is stable, the police write.
A suspected perpetrator was identified by witnesses and was arrested on the spot. The police received the alarm at around 17.45 as a suspected assault.
According to the police, the victim and the suspected perpetrator are acquaintances who have known each other previously.
