ABC News’ Olivia Katrandjian reports:

The Occupy Wall Street protests enters its third week today, following hundreds of arrests in New York late  Saturday night.

More than 700 demonstrators were arrested as the protests spread to the Brooklyn Bridge, closing down a lane of traffic for hours, New York City police said.

Police said they allowed the demonstrators to march on the bridge’s pedestrian walkway, but arrested those who marched on the car lanes, blocking traffic on one of the main routes out of lower Manhattan.

Protesters said they were ordered by police to walk in the road.

“We were peacefully walking on the top, on the wooden part, where we’re supposed to, until directed by the New York City police to go down into the street area,” said protester Gwen Goodwin told New York ABC News affiliate WABC.

“They said you had an option to walk on the street or walk on the roadway,” Aria Smith.

Protesters began blocking the bridge around 5 p.m. Saturday, and the bridge was reopened to traffic at 8:05 p.m., according to police.

“They were on the bridge blocking vehicular traffic,” said an NYPD spokesman. “They were issued multiple warnings by the police to stay on the pedestrian walkway and were told they would be arrested if they went into the vehicular lanes. Some complied but others proceeded on the Brooklyn bound vehicular walkway.”

“If they hadn’t gone into the roadway they wouldn’t have been arrested but they chose to ignore the warnings,” said the spokesman.

Police make an arrest of a protester affiliated with the Occupy Wall Street movement attempt to cross the Brooklyn Bridge, effectively shutting parts of it down, Saturday, Oct. 1, 2011 in New York. (Rose Bookbinder/AP Photo)

Police said those arrested were mainly issued summons, and only a minimal number of people are in custody.

Several members of the protest said police were making random arrests, even of people who were complying with police orders to leave the bridge roadway.

“They were allowing people to disperse if they were willing to, but they were still taking people randomly out of the line that were leaving and were arresting them,” one demonstrator told WABC-TV.

The Occupy Wall Street movement, growing to more than 1,500 people in New York two weeks after it began, had called for a march in lower Manhattan today at 3 p.m. to “show that it is time that the 99% are heard.”

“We are unions, students, teachers, veterans, first responders, families, the unemployed and underemployed. We are all races, sexes and creeds. We are the majority. We are the 99 percent. And we will no longer be silent,” read a post on the Occupy Wall Street website.

During a march through lower Manhattan last weekend, videos showed police using what demonstrators said was unnecessary force.

In some video police were seen using orange netting to contain groups of marchers, in others a man with a camera was thrown to the ground by a police officer without any apparent reason and a police officer sprayed mace on a woman.

On Friday, about 1,500 demonstrators took their protest to the New York Police Department headquarters.