Police have detained about 400 people who were protesting at the national convention of the right-wing Alternative for Germany party in Stuttgart.
German news agency dpa reported that protesters were shouting "refugees can stay, Nazis must go", as some 2,000 party members arrived at the convention centre on Saturday morning.
Demonstrators temporarily blocked a nearby motorway and burned tyres on another road leading to the centre.
Some 1,000 police officers were on the scene to prevent violent clashes between far-right party members and demonstrators.
Alternative for Germany, or AfD, has been growing in political influence as it campaigns on an anti-refugee and anti-Islam platform.