The woman, who is in her 35-year-old, was taken to hospital after the attack outside Enköping.
A person was arrested near the crime scene in connection with the operation. It's about a boy under 15 years old, according to the police.
He is not detained, but he is being handled by social services due to his age, says Tobias Ahlén Svalbro, press spokesperson for the police in Region Mitt.
An investigation with the support of LuL, the law on young offenders, has been initiated after the incident.
The boy and the woman do not have a close relationship with each other. It's too early to say anything about a motive, says Tobias Ahlén Svalbro.
The extent of the woman's injuries is unclear.
In connection with the incident, a school in the nearby area was evacuated as a precautionary measure. The police, however, view it as an isolated incident and there was no danger to the public.
