At the Lloyd Gymnasium in Bremerhaven, a high school, an amok alarm was triggered on Thursday morning.
A woman was seriously injured, but not in mortal danger, said a press spokesman for the city of the FAZ. The woman is not a teacher, but an employee of the school administration.
The woman came to the hospital.
The alleged perpetrator was arrested by the police shortly after the crime.
The police did not initially release any further details about the perpetrator and the crime.
In the short message service Twitter, the Bremerhaven police warned of a major operation in Bremerhaven's city center and called for the affected area, Mayor-Martin-Donandt-Platz and the adjacent streets, to be avoided.
The authorities set up an information phone for parents.
The independent municipality belongs to the federal state of Bremen.
Special forces searched the school to rule out the involvement of other perpetrators.
Shortly after the crime, there were rumors in the city about a second perpetrator or even a group of perpetrators.
The police measures continued, it said.
According to a police spokeswoman, the school was further searched.
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