According to initial police findings, four people were killed in a Potsdam clinic.
A 51-year-old woman was arrested on urgent suspicion, said a police spokesman on Wednesday evening.
There is a suspicion of a homicide.
One person was also seriously injured.
The police had been on duty in the Oberlinklinik in Potsdam-Babelsberg since about shortly before 9 p.m.
A homicide squad took over the investigation.
The emergency pastoral care was also on site.
The Oberlinklinik in Potsdam-Babelsberg is a renowned orthopedic specialist clinic with a total of 162 beds.
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SPIEGEL.de.
svs / dpa