The police expect up to 10,000 people to demonstrate in connection with the congress.
The demonstrators have tried to break through the roadblocks leading to the Riesa center during the morning. According to the organizers, the police have responded by beating demonstrators and using pepper spray.
The congress, which is taking place over two days, will see the AFD finalize its election platform and formally nominate the party's leader Alice Weidel as a candidate for the position of Federal Chancellor.
Currently, the AFD has around 20 percent of German voters' support, making them the second-largest party, according to the latest polls. The conservative CDU has the largest support, with around 30 percent.
The federal election will be held on Sunday, February 23.
