An ambulance parked beside a police van on a road

A 21‑year‑old woman has been arrested after a knife attack left three people injured at a Warsaw school, the latest incident in a strand of violent episodes in Polish schools this week.

Police say the young suspect used a "dangerous object" to stab a 17‑year‑old female student on the campus, while two other women – aged 17 and 24 – were hurt as they entered the building to hand in enrolment papers.

The girl who was stabbed has been taken to hospital; her condition is not life threatening, officials said. Police confirmed the attacker was a student at the school and there is no evidence she knew any of the victims.

This comes a day after police were dispatched to schools across Poland following two earlier stabbings that week, one of which took the life of a 37‑year‑old caretaker.

Authorities suggested that all of the incidents might be connected to an online challenge, and Polish police have taken sweeping security measures, arresting 76 people in the aftermath of the week‑long surge in violence.

"There is no room for compromise when it comes to the safety of Polish children and the peace in our schools," Prime Minister Donald Tusk said prior to a nationwide operation to heighten security.

Other related incidents include a 19‑year‑old student who injured nine people at a vocational school in the Mazovian province on Wednesday, and a fatal stabbing of a caretaker at a primary school in Leszczydół‑Nowiny on Thursday. The Ministry of Interior also detained a 17‑year‑old suspect in Sierpc after he allegedly said he intended to do something dangerous on school grounds.