Protests were planned in solidarity from Europe to Australia in what is being called an "International Day of Action" this weekend.
In Rome, the protests turned violent. Police fired tear gas and water cannons when some protesters hijacked the peaceful demonstration and turned it into a riot, smashing shop and bank windows and torching cars.
Clad in black with their faces covered, protesters threw rocks, bottles and incendiary devices at banks and Rome police in riot gear. With clubs and hammers, they destroyed bank ATMs, set trash bins on fire and assaulted at least two news crews from Sky Italia.
Riot police charged the protesters repeatedly, firing water cannons and tear gas. Around 70 people were injured, according to news reports, including one man who tried to stop the protesters from throwing bottles.
Fleeing the violence, peaceful protesters stormed up the steps outside the Basilica, one of the oldest in Rome. Some activists turned against the violent group, trying to stop them and shouting "Enough!" and "Shame!"
Protesters also set fire to a building, causing the roof to collapse, reports said. The Defense Ministry denied reports it was one of its offices.
Around 4,000 people marched through the streets of Berlin, with banners that urged the end of capitalism. Some marchers scuffled with police as they tried to get near the country's parliamentary buildings. In Frankfurt, continental Europe's financial capital, some 5,000 people protested at the European Central Bank, with some setting up a tent camp in front of the building.
Wikileaks founder Julian Assange spoke to protesters outside St. Paul's Cathedral in London, calling the international banking system a "recipient of corrupt money."
The London demonstration swelled to several thousand people by early evening, and police said three were arrested.
In Paris, marchers shook their fists and shouted as they passed the city's historic stock exchange, before congregating by the hundreds outside the ornate City Hall.
"Stand up Paris! Rise Up!" protesters shouted. "Sharing will save the world!"
Back in the U.S., as many as 1,000 protesters in Manhattan marched to a Chase bank branch, banging drums, blowing horns and carrying signs decrying corporate greed.
"Banks got bailed out. We got sold out," the crowd chanted.
A few protesters went inside the bank to close their accounts, but they group didn't stop other customers from getting inside or seek to blockade the business.
"We aren't going to be a part of this system that doesn't work for us," said a demonstrator withdrawing her money, 20-year-old Brooklyn College student Biola Jeje.
The demonstration was fairly orderly as it wound through downtown streets, however, police later arrested 24 people at a Citibank branch near Manhattan's Washington Square Park. Most were detained for trespassing after they ignored a request by the bank to leave, police said.
Hundreds of people marched through the streets of downtown Los Angeles, shouting slogans and waving signs under the sunny skies. The marchers gathered at Pershing Square and moved south through the city's financial district, carrying placards reading "We Are the 99%," "Bail Out People, Not Wall Street" and "Get Money Out of Politics."
Most of the protesters returned to an Occupy Wall Street encampment that's been set up outside City Hall for nearly two weeks.
The weekend brought out protesters in other parts of the country as well for smaller demonstrations, and more rallies were planned in such cities as Little Rock, Ark., Providence, R.I.; and Seattle.
Nearly 1,500 gathered Saturday for a march past banks in downtown Orlando. About 50 people ranging from college students to older people met in a park in downtown Jackson, Miss., carrying signs calling for "Health Care Not Warfare." Organizers expected more people to come and go during the day.
The Occupy Wall Street movement began last month with demonstrators voicing their frustration over many issues, including unemployment and corporate greed.
The Associated Press contributed to this report.