Tens of thousands took to the streets of the Italian capital for a march that turned violent and equal numbers rallied in Madrid and Lisbon while Wikileaks founder Julian Assange joined angry demonstrators in London.
About 50 protesters gathered outside Africa's biggest bourse, the Johannesburg Stock Exchange, to voice concern over South Africa's widening gap between rich and poor.
In Cape Town, protesters gathered in the Company Gardens behind Parliament while in Durban their counterparts gathered at City Hall. Protests were also held in Grahamstown.
Biggest show of a movement’s power yet
The protests were inspired by the "Occupy Wall Street" movement in the US and the "Indignants" in Spain, targeting 951 cities in 82 countries across the planet in Asia, Europe, Africa and the Americas.
It was the biggest show of power yet by a movement born on May 15 when a rally in Madrid's central Puerta del Sol square sparked a worldwide movement that focussed anger over unemployment and opposition to the financial elite.
"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 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."
The protests received unexpected support from Italian central bank governor Mario Draghi, a former executive at Wall Street giant Goldman Sachs who is set to take over as president of the European Central Bank next.
"Young people are right to be indignant," Draghi was reported as saying on the sidelines of talks among G20 financial powers in Paris.
"They're angry against the world of finance. I understand them," he added. But as reports of the violence filtered through, he said: "It's a great shame."
Scuffles in London
There were more protests staged in Amsterdam, Athens, Brussels, Geneva, Paris, Sarajevo and Zurich.
Thousands also rallied in New York and Washington, where they protested outside the White House and the US Treasury.
Scuffles broke out in London where about 800 people rallied in the financial district by St Paul's Cathedral, raising banners saying: "Strike back!"; "No cuts!" and "Goldman Sachs is the work of the devil!"
Three lines of police, and one line at the rear on horseback, blocked them from heading to the London Stock Exchange and pushed back against lead marchers, some wearing masks.
"I am here today mainly as a sense of solidarity with the movements that are going on around the world," said Ben Walker, a 33-year-old teacher from the eastern English city of Norwich.
Flanked by bodyguards, Assange spoke 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," he said.
The European Union also became a target for anger as the eurozone debt crisis continues, with some 9 000 protesters marching to the EU's headquarters in Brussels and rallying outside the ECB's headquarters in Frankfurt.
Just the beginning
In Rome, 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 amid a security lockdown in the Italian capital.
"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 one 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.
He said the clashes were "a very worrying signal for civil co-existence".
"The violent protesters are a very organised group that infiltrated the demonstration," Rome Mayor Gianni Alemanno told reporters.
"We've seen the worst of Europe today in Rome," he added.
Seventy people were injured in the clashes and treated by medics, including three in a serious condition, Italian news agency ANSA reported.
Backing from Italy's main trade unions and student movements boosted the numbers at the protest in Rome - in contrast to most of the other rallies.
As the day began, around 500 people gathered in the heart of Hong Kong's financial district to vent their anger. About 100 demonstrators in Tokyo also voiced fury at the Fukushima nuclear accident.
Another 600 demonstrators in Sydney set up camp outside Australia's central bank, where the plight of refugees and Aboriginal Australians was added to the financial concerns.