Los Angeles police moved into City Hall Park about at 12:30 a.m. PST Wednesday. About an hour later the area was cleared of tents and closed for cleanup, CNN reported.
About 1,400 officers participated in the operation, Los Angeles Police Chief Charlie Beck said.
WPVI-TV, Philadelphia, reported about 40 Occupy Philadelphia protesters were arrested following clashes with police.
Authorities evicted Occupy Philadelphia protesters just after 1 a.m. EST from Dilworth Plaza near City Hall. Protesters scattered and regrouped elsewhere as police gave chase.
The Philadelphia Inquirer reported at least one protester and two police officers were injured, none seriously.
A group of protesters remained near Dilworth Plaza into the night, but mounted police cleared the area, WPVI said. Philadelphia Police Commissioner Charles Ramsey said several streets were closed until further notice.
The Occupy movement began as Occupy Wall Street in New York in September. It has spread across major cities worldwide as a protest against the unequal distribution of wealth. In recent weeks, cities have begun clearing encampments, citing economic, health and public safety concerns.
In Los Angeles, witnesses said most of the demonstrators complied with the orders to disperse, the Los Angeles Times said.
Police also arrested people who refused to leave City Hall Park voluntarily.
Several protesters were found hiding in the trees, the Times said. Police used a cherry-picker to remove several protesters from their leafy perches.
One protester almost fell to the ground when a branch buckled, but instead climbed higher. Police armed with a rifle loaded with rubber bullets drew a bead on the protester and another demonstrator, officer Norma Eisenman said.
Los Angeles Mayor Antonio Villaraigosa joined Beck at the park early Wednesday to observe officers as they arrested the few Occupy LA protesters left after a police sweep of the campsite.
In a statement earlier, Villaraigosa said the Los Angeles Police Department began enforcing the closure of City Hall Park after giving protesters "a final opportunity to leave without facing arrest." The closure originally was announced Friday.
"We have taken a measured approach to enforcing the park closure because we have wanted to give people every opportunity to leave peacefully," Villaraigosa said in his statement.
While the park is closed, "a 1st Amendment area will remain open" at one set of steps to City Hall.
"Once the park is cleared, it will be repaired and returned to all Angelenos to exercise their 1st Amendment rights," Villaraigosa said.
Villaraigosa -- a former union organizer and former president of the Los Angeles chapter of the American Civil Liberties Union -- told the Times Tuesday he and Beck had made the decision to allow overnight camping on the lawn in the hope of charting a "different path" with protesters.
That was in part because he respects many of their views, he said.
He decided to order Occupy LA to leave the lawn after learning children were at the encampment, he said. He was also concerned about public health risks and damage to the lawn, which Villaraigosa estimated would cost "in the hundreds of thousands of dollars" to repair.