Police wearing helmets and carrying shields early on Tuesday began to clear Zuccotti Park in New York City's financial district, where protesters from the Occupy Wall Street movement have been camped since September.
The office of New York City Mayor Michael Bloomberg said the protesters should temporarily leave the park and remove their tents and tarps. The protesters said hundreds of police were mobilizing around the park and that the eviction of the demonstrators was in progress.
Police spokesman Paul Browne said the city and the owners of the park, Brookfield Office Properties, issued fliers to the protesters saying the park would be cleared for cleaning shortly after 1 a.m. (6 a.m. British time).
Browne said 15 people had been arrested for disorderly conduct and resisting arrest.
The flier said the city and Brookfield 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.
Browne said most people had left peacefully, but there was still a small group of people in the middle of the park refusing to leave. He said the protesters can return if they want after the park is cleared but without their tents and belongings.
Authorities set up bright lights at the park and sought to keep people away from the site as police surrounded it.
Protesters set up camp in Zuccotti Park on September 17 to protest a financial system they argue mostly benefits corporations and the wealthy. The Occupy Wall Street movement has sparked similar protests against economic inequality across the country, and in some cases have led to violent clashes with police.
Samantha Tuttlebee, 35, from the Brooklyn section of the city, said she was volunteering at the protesters' medical tent at the park when the raid happened. She said she had not been living at the park.
I'm shocked. They put my arms behind my back. They are really violent, Tuttlebee said. We were trying to leave and they threw us out.
Police on Monday moved into an encampment by anti-Wall Street protesters in Oakland, California, clearing out occupants and taking down tents, while in Portland, Oregon, police confronted an estimated 1,000 protesters on Sunday.
The protesters in Wall Street had said they hope on Thursday to shut down Wall Street -- home to the New York Stock Exchange -- by holding a street carnival to mark the two-month anniversary of their campaign against economic inequality.