Foley Square is extremely packed with protesters at the moment, some initial guesstimates put the crowd somewhere in the neighborhood of 5,000 to 10,000. It's so crowded that it's difficult to move, and a few protesters have been arrested—one was bleeding from the mouth. There are reports that an NYPD officer injured his ankle; it's unclear what caused the injury. The police are not letting protesters into Foley Square from most sides, and arresting those who spill off the sidewalks across the street from the square. The Other 99 is operating a live video stream from the rally.

One protester at the park says, "I can actually feel the ground shaking." The original plan was for the rally to march over the Brooklyn Bridge, and we've heard nothing to suggest that isn't happening. We'll update with more information as the protest unfolds.

Update 6:10 p.m.: The march is underway, but it's proceeding very slowly because the NYPD has set up kettle nets along the route and they're not letting protesters though, except through a small number of openings.

And City Councilman Juamaane Williams just Tweeted, "I have just been #handcuffed & #arrested by the #NYPD, practicing #civildisobedience with #OccupyWallStreet & the #99percent." His Tweet before that was "We are sitting on the approach to the #BrooklynBridge, standing up for the #99percent and for #equality." You may recall that Williams was arrested after the West Indian-Amercian Day Parade by apparently overzealous cops who didn't believe he was a Council member.

Here's video of the crowd at Foley Square:

Update 6:25 p.m.:CBS2 is streaming live aerial footage of the entrance to the bridge. CBS's @LouYoungNY is reporting that Foley Sq protesters "are only being allowed to march north, i.e. away from Bk Bridge." At this point, it's unclear if the march is being allowed onto the pedestrian walkway on the bridge. The protesters, as they wind their way through the streets, are chanting, "Who took the money? Wall Street! And who's gonna pay? Wall Street!"

The Other 99 livestream just showed the side of a WPIX 11 News van, on which someone had written graffiti "TELL THE TRUTH." Some marchers are worried that the NYPD is planning to trap them by the bridge and make mass arrests. By some estimates, approximately 100 protesters have been arrested already, including Councilmember Williams, and have been loaded onto buses by the bridge.

Update 6:38 p.m.: The massing march is proceeding across the pedestrian walkway on the Brooklyn Bridge as planned. Thilman tells us, "Thousands are pouring onto the Brooklyn Bridge, many carrying battery-powered 'candles.' " There are unofficial reports that the Brooklyn-bound roadway is closed to cars. It's unclear where they're headed on the other side (Junior's, anyone?), but the protesters say the bridge march is intended to "culminate in a festival of light as we mark the two-month anniversary of the Occupy movement, and our commitment to shining light into our broken economic and political system."

Update 6:50 p.m.: Now, there are projections against buildings (including a city building and the Verizon building) that say "We are the 99!%" and then changes to "Look around, you are part of a global uprising! Happy birthday Occupy Movement"! Then it flashes the word "Occupy" and names every city that has an Occupy movement. It's an energizing moment—Thilman says, "I've never seen everyone so jubilant."

Cars are honking support to the marchers:

And Bucky Turco says the first wave of marchers have made it halfway across the Brooklyn Bridge.

Update 7:30 p.m.: Thilman tells us the crowd was singing, "Happy birthday, Dear Occupy." He adds there doesn't seem to be a police presence on the bridge and that he overheard a man say to his wife/companion, "...a crowded protest is no excuse for an inappropriate touch!"

Update 9:30 p.m.: Here are some videos of the the projections:

(On the scene reporting from James Thilman)