Protesters from unions, civil society groups and left-wing parties gathered in the eastern city of Erfurt as large numbers of police, including reinforcements from across Germany, were deployed ahead of the AfD's two-day conference. AfD stands for Alternative for Germany.
Watched by police in riot gear, protesters sat in rows to block highways and roads leading to the convention centre where the meeting is being held.
Police estimated about 15,000 people joined demonstrations in and around the eastern city on Saturday.
The AfD launched the event by re-electing party chiefs Alice Weidel and Tino Chrupalla, under whose leadership the AfD has surged to the top of national opinion polls ahead of Chancellor Friedrich Merz's conservatives.
The opening speeches mocked and lambasted the protesters as anti-democratic. They revelled in the AfD's rise that could see the party taking power in regional elections in 2026 for the first time, while painting their mainstream rivals as tired, out of touch and leading Germany into decline.
"For this remains our last chance to save our country," Weidel said. "More and more people in this country want to support us in the fight against Germany's decline, in the fight for our fatherland and for our identity."
Underscoring the party's hard line on immigration, a song called "Send them back" played on the AfD's social media stream minutes before the convention opened.
Inside the convention centre, vintage-style cards were on sale with slogans such as "YOU will be deported".
The conference comes ahead of elections in two eastern states which the AfD hopes will help pave the way for success at a national level, a prospect that has alarmed its opponents.
"We want to make it clear that we simply won't tolerate this, that fascism is on the rise here in Germany," said Georg Becker, a spokesperson for Widersetzen ("Resist"), an anti-AfD umbrella group behind the Erfurt protests.
