The demonstration was part of a four-day-long "Blockupy" protest, due to run until Saturday, against capitalism and austerity measures implemented to tackle the euro zone crisis.

"Hungry? Eat a banker," read one banner protesters held up outside the Messeturm skyscraper, housing Goldman Sachs offices. Reuters' Frankfurt office is also in the building.

Police closed off the road outside the Messeturm - a main artery into Frankfurt - and flooded it with officers. They far outnumbered the group of some 50 protesters, and began detaining them. There was no violence.

Police said they detained 40 activists elsewhere in Frankfurt.

The protesters are angry at the misery they say governments are inflicting on people with their response to the crisis, which has intensified since inconclusive elections in Greece this month fuelled concerns about its future in the euro zone.

Friday's protest followed a legal scrap between activists and authorities over whether the demonstrations should be allowed to go ahead. A court on Monday gave the go-ahead for a rave on Wednesday and protests on Saturday but ruled against them taking place on the other days.

On Thursday, police said they detained 150 demonstrators for defying the protest ban. On Wednesday, they peacefully removed demonstrators from outside the European Central Bank's Frankfurt headquarters.

The ECB reported no trouble on Friday and commercial banks, many of whom have made contingency plans to cope with the protests, said their operations were running smoothly.

"Our operating business is not curtailed. We were well prepared," said a Commerzbank (CBKG.DE) spokeswoman.

Police sealed off Deutsche Bank's (DBKGn.DE) headquarters. Germany's biggest bank said its business was unaffected.

The ECB is at the centre of the policy response to the crisis and has faced calls from politicians, investors and protesters to do more.

The central bank says it has already headed off a major credit crunch with unprecedented funding operations in December and February, and is putting on the onus on governments to act.

Frankfurt police have drafted in reinforcements from other German states to cope with the protests. Some 5,000 police are ready to be deployed.

(Reporting by Paul Carrel, Edward Taylor and Arno Schuetze; editing by Andrew Roche)

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