Members of the far-right Alternative for Germany (AfD) gathered Saturday to vote on new leadership after the party's triumphant turnout in September's general election.
The AfD captured nearly 13 percent of the vote and almost 100 seats in parliament -- a watershed moment in postwar German politics that left Chancellor Angela Merkel the winner but required her to seek out a still-elusive coalition.
But a festering row between radical nationalists and more moderate forces has roiled the AfD's top ranks, with co-leader Frauke Petry abruptly quitting just days after the election to form her own breakaway party.
About 600 delegates at the two-day congress in the northern city of Hanover were to vote on a replacement for her as well as a new board, determining the ideological direction of the party.
Outside, hundreds of demonstrators staged sit-ins to block roadways to the venue, delaying the start of the congress by nearly an hour.
After reporting minor scuffles with protesters, police deployed water cannon in frigid weather to remove some of the blockades.
Several officers were injured in scuffles, one on the hand by a flying bottle, and a demonstrator who had chained himself to a barricade suffered a broken leg and was taken to hospital, police said.
Later Saturday more than 5,000 pro-refugee demonstrators marched through the city centre supporting Merkel's liberal border policy, which has allowed in more than one million asylum seekers since 2015. Another anti-AfD rally by trade unionists was expected to draw around 3,000 people.
AfD leader Joerg Meuthen, who has allied himself with its hard-right nativist wing, has said he will stand for another two-year term.
He told cheering delegates that the AfD was Germany's "only party for patriotic policies" and accused Merkel of "fundamental political failure" during her 12 years in office.
Launched as a populist anti-euro party in 2013, the AfD has veered sharply to the right since then and campaigned for the September election with slogans such as "Bikinis Not Burqas", "Stop Islamisation" and the ubiquitous "Merkel must go".
It is now represented in 14 of Germany's 16 state parliaments but has been shunned by mainstream parties as a potential partner at the national level.
A video shown at the start of the event celebrated the regional election victories and ended with the rallying cry "We want our homeland back."
Meuthen predicted the AfD would hold seats in all 16 states by the end of 2018.
The fractured political landscape has made it more difficult than ever for Merkel to cobble together a governing majority.
Talks to form a coalition spanning the political spectrum for her fourth and probably last term broke down in acrimony last month.
She is now trying to woo the centre-left Social Democrats back into a right-left "grand coalition" government.
If she is successful and averts a snap election, the AfD would become Germany's largest opposition power, strongly boosting its profile.
Meuthen said the "pathetic little sandbox games" of the other parties leading to the political deadlock in Berlin were helping the AfD.
"It is good for us," he said to applause. "It brings us more supporters."
Delegates will debate a motion to have Meuthen as the AfD's sole president.
Meanwhile more centrist forces in the party are backing the party's Berlin chief, Georg Pazderski, a former army colonel, as co-leader.
But speculation was rife that the party's powerful parliamentary group chief, Alexander Gauland, could mount a leadership challenge.
The list of motions to be debated in Hanover offered a snapshot of the party's priorities.
They included a call for Germany to ban circumcision of male babies, targeting a common practice among Muslim and Jewish families, and a condemnation of a new definition of anti-Semitism adopted by parliament which it considers a "curb on free speech".
The party recently sparked outrage by calling for the immediate return of tens of thousands of Syrian refugees in Germany, claiming that "large parts" of the war-ravaged country were now safe.