The city of San Francisco leased an abandoned school for protesters to use as an alternative campsite [Reuters]

San Francisco police have arrested 85 "Occupy" protesters after dismantling an encamptment they had built in an overnight raid.

The raid began before daybreak on Wednesday, when dozens of police cars, fire engines and ambulances surrounded the campsite at Justin Herman Plaza and blocked off the area. City officials previously declared the site, near the Californian city's financial district, a risk to public health.

Police didn't immediately say how many people were in the plaza at the time, but campers put the estimate at 150.

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"Most of the protesters went peacefully," but one officer received minor injuries when two people threw a chair that cracked his face shield, said officer Albie Esparza. They were arrested on suspicion of assault.

Dozens of others were arrested for illegal lodging in the plaza and failure to disperse.

Esparza said about 15 people arrested on charges ranging from resisting arrest to assault with a deadly weapon were still in custody.

Jack Martin, a protester based in the camp, said he was trying to leave the plaza when he was zip-tied, taken to a police station, charged and released.

Officers trashed his tent and personal belongings, he said.

Richard Kriedler, an Occupy SF organiser, said some protesters were injured, but offered no details.

"This is a very emotional town. We have anarchists, we have very emotional people that this is not going to go over well with, and this could have been handled a lot better," he said.

The protesters had been camped in Justin Herman Plaze for two months.

Alternative campsite

In a statement, Ed Lee, San Francisco's mayor, said the city had taken a "measured and balanced approach", including making an alternate site available to protesters.

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That site - an abandoned school - included a parking lot where the protesters could maintain their encampment, a classroom for meetings and two bathrooms.

The city had taken out a six-month lease on the property and offered to send city trucks to help the occupiers move to the new location. It had given the protesters until December 1 comply.

The movement against economic disparity and corporate greed began with Occupy Wall Street in New York almost three months ago, and police have removed Occupy demonstrators there and in a number of other cities.

In some cases, police used pepper spray and tear gas to get protesters to leave the camps, which many cities declared health hazards and accused of interfering with local businesses.

Source: Agencies