Police in riot gear and biohazard suits removed anti-Wall Street activists from an encampment outside the Los Angeles City Hall on Wednesday, arresting at least a dozen people as they enforced the mayor's eviction order.

Busloads of police closed in on the 8-week-old camp after midnight and declared the hundreds of protesters congregated on the lawn, sidewalks and streets around City Hall to be an unlawful assembly, ordering them to disperse or face arrest.

The Los Angeles encampment, which officials had tolerated for weeks even as other cities moved in to clear out similar compounds, was among the largest on the West Coast aligned with a 2-month-old national Occupy Wall Street movement protesting economic inequality and excesses of the U.S. financial system.

Except for some minor initial scuffles, the crowd remained boisterous but peaceful.

At least 20 protesters quit the area immediately, carrying tents and other belongings out of the camp, followed by a number of others escorted out by police.

Officers then swept into the park, arresting those who refused to leave and dismantling the camp. Tents were pulled down and flattened after police peeked inside each with a flashlight. At least a dozen people were seen handcuffed within 90 minutes after police moved in.

City officials had hoped to keep the timing of the widely expected eviction operation under wraps.

But live local television footage revealed large numbers of police, patrol cars, buses and other vehicles massing at Dodger Stadium, a few miles away, ahead of the raid. Those images prompted supporters to stream into the area in a show of solidarity with the activists.

The crowd grew steadily more raucous before police arrived with protesters chanting Move your feet, Occupy the street! Several demonstrators climbed into trees, and fireworks were set off.

One protester, Anthony Candelaria, 21, a Los Angeles college student among the crowd gathered at City Hall, said before the raid began that he planned to hold the fort down until they drag us out by our feet.

By contrast, about 100 Occupy protesters in Philadelphia peacefully vacated their camp early on Wednesday after police moved in and warned protesters they faced arrest unless they left on their own, police said.

'MEASURED APPROACH'

Shortly after the eviction in Los Angeles began, Mayor Antonio Villaraigosa, who had initially welcomed the protesters, issued a statement saying the city was taking a measured approach to enforcing the park closure.

We have wanted to give people every opportunity to leave peacefully. I ask that anyone who remains in the park to please leave voluntarily, he said.

Protesters began moving onto the City Hall park on October 1, and within weeks the encampment had grown to include as many as 500 tents, with between 700 to 800 full-time residents.

Their number diminished sharply after Los Angeles Mayor Antonio Villaraigosa announced last week that he wanted protesters to pack up their tents and other belongings and leave by Monday or face forcible removal.

Villaraigosa had been friendly toward the protesters, even supplying them with ponchos for inclement weather. But as city officials complained of crime, sanitation problems and property damage, the mayor decided the group had to go.

Since the eviction deadline passed, the status of the camp had remained in limbo. Attorneys for Occupy LA asked a federal judge for a court order barring police from shutting it down, arguing city officials had violated their civil rights by ordering the camp dismantled. The judge has made no ruling.

Villaraigosa issued his eviction notice last Friday after talks on a plan to induce the protesters to leave voluntarily collapsed, setting the stage for the latest showdown between leaders of a major U.S. city and the Occupy movement.

The mayor has promised to find alternative shelter for homeless people who had taken up residence at City Hall and were estimated to account for at least a third of those camped there.

(Writing and additional reporting by Steve Gorman; Editing by Cynthia Johnston and Jackie Frank)