A man has been arrested after punching the new mayor of Germany's southwestern city of Freiburg as he was celebrating his election win.

The Sunday night attack was the latest on a politician in Germany after the stabbings of a mayoral candidate in Cologne and the mayor of the small western town of Altena in recent years.

Independent candidate Martin Horn, 33, suffered a broken nose, a broken tooth and bruises. Hours earlier he had won a runoff against longtime Green party incumbent Dieter Salomon.

A spokeswoman for Freiburg police says the 54-year-old suspect's motivation isn't known but that he is known to have psychological problems.

Laura Riske told broadcaster n-tv on Monday that "at the moment we are working on the assumption that there was no underlying political motivation."