Helicopters hovered, shining spotlights on a downtown Atlanta park where police arrested more than 50 Occupy Wall Street protesters who had set up an encampment for about two weeks.

Streets were barricaded around Woodruff Park where -- like in many American cities -- protesters had camped out to rally against what they see as corporate greed and a wide range of other economic issues. Before police marched in, protesters were warned a couple times around midnight to vacate the park or risk arrest.

Organizers had instructed participants to be peaceful if arrests came, and most were, though police did drag out a few. Many gathered in the center of the park, locking arms, and sang "We Shall Overcome," until police led them out, one-by-one to waiting buses. Most left on foot, handcuffed with plastic ties.

Police included SWAT teams in riot gear, dozens of officers on motorcycles and several on horseback.

"It's real simple: This is a crisis of priorities that this small group of campers ... is the greatest threat in this city. It's outrageous," said organizer Tim Franzen.

Mayor Kasim Reed on Monday said he planned to revoke the permit allowing Occupy Atlanta protesters to live in the park, but was vague about when that might come.

Late Tuesday, police started surrounding the park at a busy intersection, and some protesters gathered up their tents, pillows, sleeping bags and other belongings, saying they didn't want to lose them. Right after the order to leave, some did, standing outside the barricades.

Hundreds of others stood on Atlanta's famous Peachtree Street, booing police. They shouted "Shame!" and "Who do you protect? Who do you serve?"

Reed said he was upset over an advertised hip-hop concert that he said drew 600 people to the park over the weekend but didn't have a permit and didn't have security guards to work the crowd, calling it irresponsible. Members of Reed's staff were at the scene of the arrests and many said the mayor had also arrived and might give a statement.

As police moved in, protesters chanted, "Who's park, our park," and "We are here, we are stronger, we can't take it any longer."

TV images showed the number of police far outnumbering the protesters.

The arrests in Atlanta appeared peaceful. In Oakland, Calif., police shot tear gas in response to rock throwing from some of the demonstrators who had gathered there, authorities said.

Gloria Tatum, 68, watched the arrests from behind the barricades and said, "This is a real movement."