A 15-year-old boy wielding a knife and wearing a helmet-mounted camera attacked a Polish primary school he used to attend, allegedly killing one employee and wounding two others in the country's second school stabbing in two days.

Authorities are investigating whether the attacks are connected to an online challenge encouraging teenagers to kill as many people as possible.

Police said a 37-year-old woman who worked as a caretaker died in the Thursday morning attack at the school in Leszczydol-Nowiny, northeast of Warsaw.

The school's head teacher, Krzysztof Ochmanski, was injured while subduing the teenager, officials said. Ochmanski told a radio station he heard a scream and ran into a hallway.

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"He wounded me with the blade of a rather long knife — he had three knives on him — and hit me with the handle," Ochmanski told the public broadcaster Polskie Radio RDC. "By then, I had managed to restrain him."

The day before the latest attack, a 19-year-old allegedly wounded 10 people, including himself, at a school in Ostroleka, which is in northeastern Poland.

Also this week, police arrested a 17-year-old in Sierpc in north-central Poland after authorities suspected he was planning a similar attack, Reuters reported.

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"We fear a grim copycat phenomenon," Prime Minister Donald Tusk told an emergency meeting, according to Reuters. "We are facing an extraordinary situation. ... For the first time, we are dealing with a killer who wore a helmet-mounted camera, intending to film the knife attack."

Tusk ordered police to visit schools every day to discourage further violence.

Nikola, the 18-year-old sister of a boy at the school that was attacked Thursday, told Reuters there were rumors about the social media challenge that the police are now investigating.

"I mean, I didn't know if it was even real — I still don't know if it's true, actually — because it sounds so unreal, so terrifying, just like something out of a movie: some kind of challenge to kill as many people as possible," she said.