A Jewish student was taken to hospital after repeatedly being struck on the head with a spade by a man outside a synagogue on Hamburg on the second day of Succot.
The assault came a year after a gunman killed two people in an attempted attack on the synagogue in Halle, Germany, on Yom Kippur.
While some media outlets said the victim was male, the English-language site The Local reported it was a 26-year-old woman.
The student was said to have sustained significant injuries and was given first aid by passers-by before being taken to hospital.
Police guarding the Hode Weide Synagogue arrested a 29-year-old man wearing a military-style uniform. A piece of paper with a swastika was found in a trouser pocket, according to the news agency DPA.
German Foreign Minister Heiko Maas condemned the attack as “repugnant antisemitism”.
Ronald Lauder, president of the World Jewish Congress, said he was saddened to learn that a German Jewish community was again “confronting a violent attack of terror”.
He added, “While thankfully, police on the scene acted quickly to stop the attacker from committing further violence, the security presence was not enough to deter this attacker from gravely injuring someone.
“We must ask ourselves, and German local and national authorities must address the question – why does this keep happening? Why is antisemitism thriving, and why does anyone believe there is room for such hate?”
The Halle attack took place on October 9 last year when a gunman, after failing to force entry into a synagogue, shot and killed a passer-by and then a man in a nearby kebab shop.