350 protesters have been arrested in clashes outside the new European Central Bank headquarters in Frankfurt.
Up to 10,000 demonstrators are expected to take part in rallies to coincide with the opening of the ECB's €1.3 billion tower.
Tear gas and water cannons have been used in an attempt to break up the violence.
Several cars have been set on fire – and one police officer has been injured by rioters throwing stones.
