On Sunday evening, Mayor Antonio Villaraigosa reiterated an ultimatum that the city's tolerance of the eight-week occupation would end at midnight.
"While Occupy L.A. has brought needed attention to the economic disparities in our country, an encampment on City Hall grounds is simply not sustainable indefinitely," he said in a statement.
PHOTOS: Occupy L.A.
The mayor also sought to allay concerns over a confrontational midnight sweep. Police would "allow campers ample time to remove their belongings peacefully and without disruption," he said.
Some protesters had already begun to tear down their tents Sunday afternoon. But many more announced their intention to stay put, and supporters arrived throughout the afternoon and evening, swelling the camp's ranks.
Protesters were planning to rally at 11 p.m. and remain throughout the night.
As of Sunday, Occupy L.A. had become the nation's largest remaining around-the-clock outpost for a nationwide movement that arose when the loose-knit group Occupy Wall Street moved into a park in the financial district of New York City. Police there swept in Nov. 15 and roughly removed demonstrators who refused to disperse after nearly two months.
Police also have been accused of heavy-handed tactics in dislodging occupiers in Oakland and at UC Davis and UC Berkeley, among other places. In Los Angeles, authorities were at pains to stay on good terms with demonstrators over the eight weeks. But authorities weren't prepared to let the encampment go on indefinitely.
"I am proud of the fact that this has been a peaceful, nonviolent protest," Villaraigosa said. "It has been peaceful because we have done things differently in Los Angeles."
The political stakes are high for Villaraigosa, who could suffer fallout if anything went wrong — such as being too soft or too harsh on protesters.
The movement itself can and must persist locally and nationally, said Maria Elena Durazo, head of the L.A. County Federation of Labor.
"While the tents may come down, the actions against Wall Street and the banks will rise," Durazo said.
Some participants in Occupy L.A. said that forcible removal would not prevent them from trying to reclaim their ground.
"We will remain occupiers," said Julie Levine, who served as one of several Occupy spokespeople on Sunday. "It's a symbol of the discontent in the nation and the world."
Others said that if removed from City Hall, the encampment would spread to multiple sites.
L.A. officials have offered daily gathering space, until 10:30 p.m., on the west steps of City Hall. And on Sunday, City Councilman Bill Rosendahl pledged that a committee would attempt to pursue the movement's goals within city government. That agenda includes divesting from major banks that have played a role in the nation's foreclosure crisis.
"We want a peaceful transition from this land to action," Rosendahl said.
His midday Sunday pitch to take the movement indoors — and into established politics drew a sometimes combative reception.