More than 20,000 people on Saturday joined a march through the centre of the German financial capital Frankfurt, police said, in a protest against European austerity programmes. It was the only demonstration of the anti-capitalist movement known as \"Blockupy Frankfurt\" authorised by the city and justice authorities. Previous protests over the past four days were banned by city officials and led to mass arrests. Organisers put Saturday\'s turnout at more than 30,000 with demonstrators brandishing placards saying \"The eurozone is in ruins\" and \"When unfairness becomes the rule, resistance becomes a duty\". \"We\'re very happy with the turnout,\" said Roland Suess of Attack Germany which is part of the movement. Since Wednesday, about 5,000 police have been deployed in Frankfurt. Several protests on Friday took place outside the European Central Bank\'s huge Eurotower building, as well as in the city centre, leading to the arrests of some 400 demonstrators. Police said most demonstrations passed peacefully, while some activists claimed those who had been arrested were left for hours in police buses. The anti-capitalist movement, modelled after \"Occupy Wall Street\", had staged its demonstrations seeking to paralyse Germany\'s financial centre and hinder the work of private banks and the ECB. Police identified about 1,000 apparent \"Black Bloc\" protesters wearing dark hoods, sunglasses and scarves. Such protesters are sometimes known to initiate violence and vandalism at demonstrations but they were dispersed without major incident Saturday. The police said they were \"very satisfied\" with the demonstration and congratulated themselves for preventing a repeat of the violence at an anti-capitalist rally on March 31.