Police cars were set alight and officers injured during anti-austerity protests in extraordinary scenes that brought carnage to the streets of Frankfurt.
As the bulk of protesters conducted themselves peacefully ahead of a rally in the city's main square to protest to blockade the inauguration ceremony for the European Central Bank's (ECB) new headquarters in the city, riot police confronted others in violent scenes.
Police said one officer was injured by stones thrown near the city's Alte Oper opera house, several private vehicles were burned overnight, and two police cars were set on fire at a police station in the city centre.
Another police vehicle smoldered a block from the ECB.
The fires cause black smoke to billow out across the city, the heart of Germany's finance industry.
Hundreds of officers ringed the ECB headquarters ahead of the inauguration ceremony. Protesters are targeting the ECB because of the bank's role in supervising efforts to restrain spending and reduce debt in financially troubled countries such as Greece.
The Blockupy alliance says activists plan to try to blockade the new headquarters and to disrupt what they term capitalist business as usual.
Some 10,000 people were expected for a rally in Frankfurt's main square, the Roemerberg. Organisers have chartered a special train bringing demonstrators from Berlin and are busing in others from around Germany and other European countries.
The ECB, along with the European Commission and International Monetary Fund, is part of the so-called "troika" that monitors compliance with the conditions of bailout loans for Greece and other financially troubled countries in Europe.
Those conditions include spending cuts and reducing deficits, moves that are aimed at reducing debt but have also been blamed for high unemployment and slow growth.
ECB President Mario Draghi has called for more spending by governments that are in good financial shape, such as Germany — a call that has been mostly ignored by elected officials.
The ECB said it planned to be "fully operational" during the protest, although some employees may work from home.