Kierwiński said police detained the teenager on Wednesday after receiving information from local teachers that he had spoken at school about plans to hurt someone.
Police found two knives that they said had been prepared for an attack, as well as information on the teenager's electronic devices indicating that he had searched online for ways to stage a violent attack, Kierwiński said.
Officers said a teacher at a local school alerted authorities after hearing that the student had told classmates he planned to "do something bad at school."
Police entered the home where the teenager was staying early on Wednesday and found two knives in a small bag, reporters were told.
They also seized his cellphone, which contained information about the planned attack, state news agency PAP reported.
The teenager was detained.
On Wednesday, a 19-year-old student attacked schoolmates and teachers with a knife at a vocational school in the northeastern Polish city of Ostrołęka, injuring nine people before fleeing the scene, authorities said.
Prosecutors said police later found a homemade explosive device in his backpack that he had attempted to detonate at the school.
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Source: IAR/PAP