German riot police have clashed with AntiFa in Hamburg on Thursday evening as world leaders arrived ahead of Friday’s G20 summit.
Police fired water cannon at a march attended by thousands carrying banners with slogans such as “Welcome to hell” and “Smash G20”.
World leaders including US President Donald Trump are in Hamburg for talks on a wide range of issues.
They face their own disagreements, including over climate change and trade.
TV pictures showed masked black-clad anti-capitalist activists hurling bottles, stones and other objects at police in riot gear. Medics were seen treating several people. Other protesters were building makeshift barricades on streets.
Up to 100,000 protesters are expected in Hamburg during the summit. Earlier, police had warned of possible violence and said they had confiscated a number of homemade weapons.