Demonstrators from trade unions, civil society groups, and left-wing parties staged sit-ins outside the convention center to halt the two-day event.

A large deployment of police in riot gear, including reinforcements brought in from across Germany, watched the blockades unfold.

Activists expressed deep concern over the party's rising momentum in the polls.

"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.

The mass demonstration comes at a critical political juncture. The AfD currently leads opinion polls in several eastern states, positioning the party to make historic gains in the upcoming regional elections.