Wikileaks founder Julian Assange joined around 800 people at a heavily policed rally in London's financial heart on Saturday as part of world protests against corporate greed and budget cutbacks.
The demonstrators, some of them masked, were pushed back by police as they tried to march from St Paul's Cathedral to the London Stock Exchange.
Assange, flanked by bodyguards, got a warm reception from the demonstrators as he addressed them from the steps of the cathedral.
"One of the reasons why we support what is happening here in Occupy London is because the banking system in London is the recipient of corrupt money," the Wikileaks founder told demonstrators.
The marchers, bearing banners reading "Strike Back", "No Cuts" and "Goldman Sachs Is the Work of the Devil", were ringed by three police cordons while mounted officers and vehicles also stood by.
But the protest, to the sound of guitars and drums, was overwhelmingly peaceful and the cathedral remained open to visitors, though the nearby underground station was closed.
After London's police were severely criticised for being caught out by the riots in August, they were clearly taking no chances Saturday and were out in force.
But there were only minor scuffles with one person arrested for assaulting a police officer, a spokesman at Scotland Yard said.
"The protest is largely peaceful," the spokesman added.
Organisers in a group calling itself OccupyLSX were hoping for thousands of participants after some 15,000 people expressed support on Facebook and Twitter.
Ben Walker, 33, a teacher from Norwich, eastern England, was carrying a rolled-up sleeping bag and said he planned to spend one or two nights in the area.
"I'm here today mainly as a sense of solidarity with the movements that are going on around the world," he told AFP. "We're hoping for a kind of justice in the global financial system."
Adam, a London-based student in his twenties from the United States, said he had already taken part in the Occupy Wall Street movement in New York.
"I see this as a global movement. The banking systems and economies of the world are all inter-related now, he said.
He was one of a number of foreign students at the rally: others came from Greece, Spain and South Korea.
Inspired by the Occupy Wall Street movement and Spain's "Indignants", people began taking to the streets across the world Saturday, targeting 951 cities in 82 countries.
It was the biggest show of strength yet by a movement born on May 15 when a rally in Madrid's central square of Puerta del Sol sparked a protest that spread internationally.
Dominated by anger over unemployment and opposition to the financial elite, the protests coincided with a Paris meeting of G20 financial powers preoccupied by the eurozone debt crisis.