Hundreds of New York City Police officials raided Zuccotti park here, ground zero for the anti-Wall Street protests, ordering protesters to leave the area or court arrest.
However, New York mayor Michael Bloomberg's office urged the protesters to "temporarily" leave the area, saying they could return later.
"Occupants of Zuccotti should temporarily leave and remove tents and tarps. Protesters can return after the park is cleared," the office said on the micro-blogging website Twitter.
Police arrived in riot gear with helicopters hovering above the city's financial district in the wee hours today as it began its clampdown on the two month long protests against corporate greed.
Police spokesman Paul Browne said the city had issued fliers to the protesters saying the park would be cleared after 1 am (local time) tonight.
The flier said the city had decided "that the continued occupation of Zuccotti Park posed an increasing health and safety hazard to those camped in the park, the city's first responders and the surrounding community".
Protesters were giving minute by minute update of the police action on the Occupy Wall Street website with posts including 'NYPD reporter arrested', 'Occupiers who have been dispersed are regrouping at Foley Square', 'Press barred from entering Liberty Square', 'Pepper spray deployed -- reports of at least one reporter sprayed', 'Massive Police Presence', and 'Helicopters overhead'.