Around 250 protesters have set up camp in central London, promising to occupy the site indefinitely, while 175 demonstrators in the US city of Chicago have been arrested as "Occupy" protests continue across the globe.
The events came after Saturday's Global Day of Protests - inspired by the Occupy Wall Street movement - drew crowds of supporters in cities as far apart as Toronto, Rome, Seoul and Sydney.
The London group camped outside St Paul's Cathedral in the heart of the British capital began their protest on Saturday, when several thousand tried to take over the area in front of the London Stock Exchange (LSE).
After being thwarted by lines of police, the group moved to the cathedral, located next to the privately-owned square housing the LSE, where they erected about 70 tents and camped out overnight.
Some said they would stay there as long as possible. "People are saying enough is enough, we want a real
democracy, not one that is based on the interests of big business and the banking system," Jane McIntyre, a protester, said.
Police in London, who were accused by protesters of heavy-handed behaviour on Saturday, reduced their presence at the site on Sunday at the request of a member of the cathedral's clergy, a spokeswoman for the demonstrators said.
Police said they would see how the protest developed and declined to comment on whether any action would be taken to remove the camp.
Across the Atlantic, following protests in Chicago, police arrested early on Sunday about 175 people who were part of a growing anti-Wall Street movement when they refused to take down their tents and leave a city park when it closed, police said.
|In-depth coverage of the global movement
About 500 people set up camp at the entrance to Grant Park on Saturday evening after a protest earlier in the day involving about 2,000, the Chicago Tribune newspaper reported.
Police said they gave protesters repeated warnings after the park closed at 11pm and began making arrests when they refused to leave.
Protesters who were arrested would be released after background checks were done to make sure they did not have any outstanding arrest warrants, police said.
They could face fines for violating a municipal ordinance.
In New York, dozens were arrested after thousands marched to the city's famous Times Square at the culmination of Saturday's day of global protests.
Police packed 71 protesters in vans after demonstrators mixed with tourists converged on the major commercial intersection, divided by police barriers.
Occupy Wall Street in New York City's Zuccotti Park
Meanwhile, in the Italian capital, Rome, a clean-up was under way after violence broke out during Saturday's anti-austerity protests there.
Tens of thousands of peaceful protesters marched in the city when violence, some of the worst seen in the city for years, erupted. Gianni Alemanno, the mayor of Rome, blamed the violence on "a few thousand thugs" who "infiltrated the demonstration".
Italian police said that at least four people had been injured in the clashes, while the ANSA news agency reported that as many as 70 had been wounded, with three in serious condition.
Allies of the prime minister, Silvio Berlusconi, blamed on Sunday left-wing sympathisers for the riots.
Senator Maurizio Gasparri, a member of Berlusconi's coalition, spoke of "dangerous proximity of some sectors of the left with the protagonists of the violence in Rome".
Berlusconi said those responsible must be identified and punished, and, in an apparent reference to the left, said: "They must be condemned by everyone without reservation."
Centre-left politicians dismissed accusations against the left and they too condemned the violence.
Elsewhere on Saturday, around 4,000 people marched through the streets of Berlin, with banners that urged the end of capitalism.
In Frankfurt, about 5,000 people protested in front of the European Central Bank.
In Paris, about 1,000 protesters rallied in front of city hall, coinciding with a G-20 finance chief's meeting.
In the Bosnian city of Sarajevo, hundreds walked through the streets carrying pictures of Che Guevara and old communist flags that read "Death to capitalism, freedom to the people".
Tens of thousands of Portuguese, angry at their government's handling of the economic crisis, also took to the streets of Lisbon. Other protests were staged in Geneva, Amsterdam, Athens, Brussels, Geneva, Zurich and Melbourne.