Police deployed water cannon and pepper spray after a gathering of some 20,000 protesters against lockdown and other coronavirus rules in central Germany turned violent, with some demonstrators throwing bottles at police.
Protesters from all over Germany converged on the central city of Kassel for the march, which was organised by the "Querdenker" - "Lateral Thinkers" - online conspiracy movement.
"Bottles were thrown and there were attempts to break through barriers," police said on Twitter.
Police said protesters disobeyed instructions they gave to help ensure people's safety, including by refusing to wear face masks and observe social distancing guidelines.
Protesters carried placards reading "No compulsory vaccination" and "Democracy will not tolerate censorship".
Marchers faced counter-protesters wearing face masks, one of whom held up a placard reading "Vaccinated".
With Germany in its fourth month of lockdown and vaccination efforts lagging compared to Britain and the United States, many people, from shopkeepers to would-be holidaymakers, are increasingly restive at the lack of a clear path to a return to normal life.
National and regional leaders are due to consult on Monday over the next steps in the national lockdown. But with case numbers rising sharply thanks to the spread of more infectious variants, many politicians are saying it is too early to ease restrictions.