Over 175 people have been arrested after police clashed with Occupy Wall Street activists outside the New York Stock Exchange.

Hundreds of protesters linked arms to block access to the NYSE building, prompting several violent scuffles to break out.

Chanting "Wall Street's closed!", "We are the 99%" and "Whose street? Our street!", about 1,000 demonstrators engaged in a tense face-off with hundreds of police, including many on horseback.

The protests were part of a "Global Day of Action" with hundreds of demonstrations planned across the US.

Police also evicted protesters in Los Angeles and Dallas, arresting dozens of people.

In London, protesters refused to budge as a deadline to leave their camp outside St Paul's Cathedral by 6pm passed, with the City of London Corporation now expected to start legal action to remove them.

After skirmishes throughout the morning in New York, up to 2,000 people regrouped in Zuccotti Park, the symbolic heart of the movement, where the Occupy camp was dismantled by police in a night-time raid on Tuesday.

The protesters were preparing for a later march joined by union members, planning to swarm the Brooklyn Bridge and disrupt evening commuter traffic.

"The numbers I've heard is something less than 1,000, but it's hard to tell because you have a group here and another group there and some go from one group to another," New York Mayor Michael Bloomberg told reporters.

"But it is not an overwhelming number," he added, saying "most people were able to go about their business."

New York Police Commissioner Ray Kelly said seven police officers had been hurt in the morning clashes and 177 people had been arrested.

The level of participation in the rallies could provide a clear indication of Occupy Wall Street's clout exactly two months since the movement sprang up to denounce corporate greed and the world's wealthiest "1%".

While the stock market opened on time at 9.30am (2.30pm Irish time), protesters managed a 45-minute blockade outside the NYSE. Police eventually intervened to break through, establishing a corridor to escort traders and workers.

Amid chaotic scenes, police then moved in to clear the street, and ensuing clashes sent police and protesters clattering to the ground.

One man was repeatedly clubbed with a police baton, while several protesters were handcuffed and dragged into police trucks.

Several groups split up and moved in different directions, deploying to choke points around lower Manhattan, blocking the area until police could move in and clear it.

At least one exasperated police officer seemed to concede to the protesters.

"They've blocked everything off. This is what happens when you kick them out of the park: you stir a hornet's nest," said the officer who would not provide his name.

"They wanted to disrupt Wall Street and they've done it."