In the Wuppertal House of Integration, an employee of the authority was probably seriously injured with a knife.
During the operation on Thursday, a threat situation was initially assumed, said a police spokesman.
An injured person was then found at the scene.
The situation is under control.
The officers arrested a suspect.
According to the city, the House of Integration connects institutions that look after immigrants and refugees in Wuppertal.
According to information from the police, the woman is seriously injured and her life is not in danger.
Paramedics took her to the hospital.
In fact, according to initial findings, a knife is said to have been used.
The police confirmed that the seriously injured person was an employee of an authority.
According to the city, the act happened in the house of integration.