(Will Stevens/AP Photo)

Some 500 demonstrators were arrested today at the Occupy Wall Street protests spread to the Brooklyn Bridge, closing down a lane of traffic for hours, New York City police said.

The hundreds of arrests come as the demonstration enters its third week, and with sympathizers in dozens of other cities across the country taking to the streets.

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

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 ABC station WABC-TV in New York.

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.