Clashes erupted in New York and Rome and protesters camped out on Sunday in worldwide demonstrations seen as a show of force by a rising global movement against corporate greed and government cutbacks.
There were rallies in 951 cities in 80 countries around the globe on Saturday in an extension of a campaign born on May 15 with a rally in Madrid's central Puerta del Sol square by a group calling itself "Indignados" ("Indignants").
"The Indignados movement rises again with global force," read a front page headline in Spain's El Pais daily on Sunday. In Italy, La Stampa said: "The world takes to the streets: united, peaceful and colourful."
"The fact is there is now clearly an international movement. Its preface was the "˜Arab Spring' seen in Cairo, Tunis and Benghazi," Eugenio Scalfari, a columnist for the Italian daily La Repubblica.
"It expresses the anger of a generation with no future and no faith in traditional politics but above all financial institutions seen as responsible for the crisis and profiteers of the damage to the common good," he said.
The biggest rallies were in Lisbon, Madrid and Rome, where tens of thousands came out. There were thousands too in Washington and New York where the "Occupy Wall Street" movement has gained momentum in recent weeks.
"I think it is very moving that the movement that was born here has extended throughout the world. It was about time for people to rise up," said 24-year-old Carmen Martin as she marched towards Puerta del Sol.
In London, scuffles broke out after a few thousand people gathered in the financial district near St Paul's Cathedral, raising banners saying: "Strike back!" "No cuts!" and "Goldman Sachs is the work of the devil!"
The founder of the Wikileaks whistleblower website Julian Assange joined the rally, telling the protesters from the steps of St Paul's: "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."
Some of the London protesters spent the night camped out in front of the cathedral in around 70 tents despite police calls for them to disperse. Participants said they intended to stay until the government responded to their demands.
Major protests took place at European Union institutions in Brussels and Frankfurt, as well as in Athens, where painful budget cuts imposed by international lenders in return for a bailout have sparked widespread anger.
In Rome, which saw the worst violence of the day, the march quickly degenerated into running street battles between groups of hooded protesters and riot police who fired tear gas and water jets into the crowd.
"Today is only the beginning. We hope to move forward with a global movement. There are many of us and we want the same things," said protester Andrea Muraro, a 24-year-old engineering student from Padua.
"Only One Solution: Revolution!" read a placard. One group carried a cardboard coffin with Italian Prime Minister Silvio Berlusconi's name on it.
Berlusconi later condemned the "incredible level of violence" at the march, which took place amid a security lockdown on Rome's major monuments.
"We've seen the worst of Europe today in Rome," Mayor Gianni Alemanno said.
Groups of protesters torched cars, smashed banks and vandalised a church in the Italian capital, hurling paving blocks and bottles at police.
Seventy people were injured and there were 12 arrests.
In New York, 88 people were arrested as police on horseback charged into busy Times Square and at least one woman was injured.
In Canada more than 10,000 blew bubbles, strummed guitars and chanted anti-corporate slogans at peaceful protests in cities across the country.
"I believe a revolution is happening," said 30-year-old Annabell Chapa, who brought her one-year-old son Jaydn along in a stroller to a rally in Toronto.
The protests received unexpected support from Italian central bank governor Mario Draghi, a former executive at Wall Street giant Goldman Sachs set to take over as president of the European Central Bank next month.
"They're angry against the world of finance. I understand them," Draghi said at the G20 meeting in Paris on Saturday, expressing regret however at the reports of violence.
In the Portuguese capital, where some 50,000 rallied, Mathieu Rego, 25, said: "We are victims of financial speculation and this austerity programme is going to ruin us. We have to change this rotten system."
There were smaller mostly peaceful protests also in Amsterdam, Geneva, Miami, Montenegro, Paris, Sarajevo, Serbia and Zurich, with protesters chanting anti-capitalist slogans and wearing satirical masks.
In Mexico, Peru and Chile, thousands also marched to protest what they slammed as an unfair financial system and stagnant unemployment.
As the day began, hundreds rallied in Hong Kong and Tokyo where demonstrators voiced their fury at the Fukushima nuclear accident.
Hundreds also set up camp outside Australia's central bank in Sydney.