Protesters began gathering Saturday in Magdeburg to rally against an estimated 1,400 neo-Nazis planning to march through the east German city.
Police said they are deploying some 2,000 officers from 10 German states to the site of the dueling demonstrations, in one of the largest police operations the state of Saxony-Anhalt has ever seen.
By morning, more than 100 anti-extremist protesters were already participating in a sit-in.
In addition to the protests, some 14,000 people were expected to attend a street party against the extreme right organized by city officials.
The occasion of the neo-Nazi march is the 68th anniversary of the bombings of Magdeburg during World War II.