Frankfurt, Germany: Thousands of anti-capitalist protesters clashed with riot police near the new headquarters of the European Central Bank (ECB) in Frankfurt on Wednesday, hours before the ceremonial opening of the 1.3-billion-euro ($1.4-billion) building.

Several cars were set on fire and streets were blocked by burning stacks of tires and rubbish bins. At least one police officer was injured, police said.

Police used water cannon to try to make a path through the mass of black-clad protesters to the entrance of the building, which is blocked off from the street by police barricades.

ECB President Mario Draghi was due to make a speech there at 11 am (0600 ET).

The organisers, a group called Blockupy - named after the Occupy Wall Street movement in 2011, estimated that about 10,000 demonstrators were at the rally. Thousands came into the German financial capital from other parts of Europe.

‘Our protest is against the ECB, as a member of the troika, that, despite the fact that it is not democratically elected, hinders the work of the Greek government. We want the austerity politics to end,’ Ulrich Wilken, one of the organizers, said.

‘We want a loud but peaceful protest,’ he told Reuters.

Frankfurt police spokeswoman Claudia Rogalski described the mood of the crowd as ‘aggressive’.

‘We've had stone throwing, burning rubbish bins and seven police cars were damaged, many set on fire,’ she said.

Blockupy says it represents grass-roots critics supranational financial institutions including the ‘troika’: the ECB, the European Commission and the International Monetary Fund, whose inspectors monitor countries such as Greece and Cyprus that have received international bailouts.

The ECB is also influential as a provider of finance to the banks of struggling countries and has in recent weeks sanctioned a drip feed of extra emergency finance to Greece's lenders.

Greek Finance Minister Yanis Varoufakis last week criticized ECB policy towards Athens as ‘asphyxiating’, a criticism also made by the protest organisers.