Robert Stolarik for The New York Times

Several protesters were arrested early Wednesday after scores of Occupy Wall Street demonstrators converged on Union Square Park in Lower Manhattan, the authorities said.

In all, six protesters were taken into custody after the hours-long face-off on a range of charges, including resisting arrest, disorderly conduct and obstructing governmental administration, according to a spokesman for the New York Police Department.

“They were blocking pedestrian traffic,” said the spokesman, who could not provide an estimate of the crowd’s size. “They were given a lawful order to disperse and when they subsequently refused, they were arrested.” The spokesman asked that his name not be used.

The police sweep prevented about 200 Occupy Wall Street protesters from sleeping in the park. Officers also seized books and other materials.

Commanders said that the books and other items were “unattended property” and could not remain on the sidewalk. Protesters claimed that the books were their property.

After a few moments of shouting back and forth, dozens of officers plunged into the crowd from two directions, shoving protesters and causing some to stumble backward and fall. Officers threw two people to the ground, including a woman who lay on her back for several minutes before an ambulance arrived to attend to her.

As protesters tried to help the injured woman, officers placed an additional line of metal barricades on a sidewalk south of the park.

A moment later, a protester darted forward and kicked a section, sending the linked barricades skidding a short distance toward the police. Dozens of police officers then rushed forward once again, pushing the barricades into the crowd, and forcing the protesters backward 40 feet or more.

Lopi LaRoe, an artist from Brooklyn, said that she was kneeling next to the injured woman when the police surged into the crowd.

“The cops reacted without order,” she said. “It was scary.”

Officers made the first arrest at about 12:20 a.m. at the southeast corner of the park on 14th Street, the police said.

Hours later, at about 4:30 a.m., five more protesters were arrested opposite 4 Union Square South, the police said.

A spokesman for the New York Fire Department said it had no record of injuries in the clash.

Protesters had gathered in Union Square Park after the police closed Zuccotti Park — the site where the Occupy Wall Street movement first emerged last year — in Lower Manhattan on Saturday night.

In the following days, they established a presence in Union Square Park, distributing literature from tables and holding meetings. Small groups of protesters slept in a plaza at the southern end of the park. Some declared that a long-term encampment was in the making.

But around midnight on Tuesday more than 100 police officers arrived at Union Square, and a commander ordered the protesters from the plaza and onto the sidewalk along 14th Street. Then, as protesters chanted “Bloomberg, beware. Zuccotti Park is everywhere,” the police placed metal barricades around the plaza as protesters objected.

“Are they going to block off every single park we go to?” asked Faith Laugier, from Spanish Harlem.

About 200 protesters milled on the sidewalk. Some lay down wrapped in blankets. Others distributed books from plastic crates. At one point, some protesters pushed over the barricades ringing the plaza, which were quickly righted by the police.

At about 2 a.m., lines of police officers pushed through the crowd on the sidewalk, ordering those sitting or lying down to get up.

Later, the police seized crates of books. They also disposed of stacks of pamphlets and fliers that could be seen being dumped into the back of a sanitation truck parked on 14th Street.

By 5 a.m., however, the officers had withdrawn to the edges of the park and the protesters once again were free to stand or sit on the sidewalk along the north side of 14th Street. Soon, more than two dozen of them once again wrapped themselves in blankets and lay down to sleep.

On Wednesday morning, Norman Siegel, a longtime civil rights lawyer, said that he had received several phone calls overnight on Wednesday. He said that some public parks, including Union Square – with a long history of civil disobedience – have a 1 a.m. curfew, but that the police tend to enforce those rules selectively, which adds uncertainty and confusion about what rights apply for peaceful protest.

He said that the rules as applied to Zuccotti Park, a privately owned public space, were being applied inconsistently as well by the police.

“We’re getting into the spring and there needs to be a meeting between Mayor Bloomberg, the police and O.W.S. and civil rights lawyers,” Mr. Siegel said. “The cornerstone of a democracy is the right to protest. We need leadership of bringing people together. The O.W.S. people are not going to disappear, and the police are here, obviously. Why stay on a road to confrontation?”

He said the tension was building between the Occupy protesters and the police officers.

“We’re going to see more demonstrations,” he said, but city leaders must work to avoid the potential for violent confrontations. “The mayor seems to have a tin ear on this.”