More than 100 police officers were deployed to break up a mass brawl in Berlin reportedly organised by two rival YouTube stars.
The fight broke out on Thursday evening in one of the main squares in the German capital, police said. Nine people were injured.
More than 400 people had gathered after two social media influencers reportedly urged their fans to join a face-off.
As tensions escalated, a large melee involving around 50 people erupted.
Officers used pepper spray and tear gas after attempts to disperse the crowds in Alexanderplatz with loudspeakers failed.
As police intervened, clashes spilled over in a nearby subway, where rocks picked up from railway lines were reportedly thrown.
Two officers were injured and six people were treated for eye irritation from tear gas, Berlin Morgenpost reports.
The brawl was the result of a "dispute" between two rival YouTube stars from Berlin and Stuttgart, according to local media reports.
Guten Morgen Hauptstadt,— GdP Berlin (@GdPHauptstadt) March 22, 2019
auf dem Alexanderplatz gab es gestern mal wieder die Zusammenkunft von zu viel Testosteron, die mehr oder weniger so gewollt war - Unser Landeschef Norbert Cioma richtet einen Appell an die Verantwortlichen pic.twitter.com/APmRICKt4d
In social media posts, the YouTubers, named as "Thatsbekir" and "Bahar Al Amood" by German media, both denied they were at fault for the brawl.
Norbert Cioma, head of Berlin's Gewerkschaft der Polizei (GDP) police union, called on social media celebrities with vast followings to be more responsible.
"We see in the rapper scene, and increasingly also with other influencers, that they are sometimes very negligent with their influence," he said.