Robert Stolarik for The New York Times

At the stock exchange in the early morning, many members of the group pushed through lines formed by police, waving signs and banging drums as they moved. The police started taking protesters into custody who had sat down on the street about a block away from the exchange.

“Sidewalk!” an officer shouted, shoving a protester out of the road.

Another protester held a sign nearby: “Tear down this Wall Street.” The demonstrators and the large deployment of police officers snarled traffic on streets around the exchange.

Protesters chanted, “We are the 99” and “We aren’t afraid of your nightsticks.”

Protesters had vowed to prevent traders from reaching the stock exchange on Wall Street, and some traders did appear to have a hard time reaching the building. But the stock exchange opened for trading as usual at 9:30 a.m.

About 10 a.m., Paul J. Browne, the Police Department’s chief spokesman, said “there are probably between 50 and 60 arrests.” Most were in the street at Nassau and Pine streets, he said.

Robert Stolarik for The New York Times

One of the more intense confrontations took place before 10 a.m. near the intersection of Broad Street and Beaver Street, where a few hundred people had gathered, dancing and chanting and brandishing black umbrellas.

A line of police officers surged into the crowd, shoving protesters to the sidewalk, grabbing some and hurling them to the ground, and using long batons to strike others with overhand blows. Officers then walked up Beaver Street pushing the crowd back. Many of the protesters moved around the corner joining another group sitting in a circle, at the intersection of William Street and Exchange Place.

About 8:30 a.m. at the corner of Nassau and Pine Streets, about 300 people stood and sat in the intersection waving flags and singing. A few minutes later, a police officer announced through a megaphone: “You’re obstructing vehicle traffic. If you don’t leave the street, you’ll be subject to arrest.”

At Pearl and Wall Streets, there were some arrests as the police tried to keep the streets sidewalks open for pedestrians. Most of the charges stemming from those arrests were for disorderly conduct and resisting arrest.

Chang W. Lee/The New York Times

Many of those taken into custody were sitting in the street at the corner of Pine and William Streets, a block from the exchange, including one woman in a wheelchair who held an American flag. Cheers rose as two police vans filled with demonstrators drove away.