The Los Angeles Police Department (LAPD) began making arrests Monday morning after Occupy Wall Street protesters camped outside city hall defied a court order to decamp.
According to police, at least 1,000 people flooded into the area around City Hall Park before the Sunday night (08:00 GMT) deadline.
"The best way to keep a non-violent movement non-violent is to throw a party, and keep it festive," protester Brian Masterson was quoted as saying by the Associated Press.
However, while the party was in full swing, some of those camped outside attended sessions on resistance tactics, including how to stay safe should police employ rubber bullets or using pepper spray. Many said they would refuse to leave and were willing to be detained.
Earlier, a Los Angeles police chief, Charlie Beck said: "I have no illusions that everybody is going to leave. We anticipate that we will have to make arrests."
By 05:00 (13:00 GMT) police said those blocking streets would be arrested, but those staying in the park would not. The protest camp inside the park has grown to an estimated 485 tents.
Officers carrying batons and less-than-lethal weapons took to the streets to break up sit-ins by angry protesters.
LAPD commander Andy Smith confirmed for Reuters several arrests had been made. Smith refused to comment on when - or if - police planned to clear City Park Hall itself.
Instead, Smith said, police were presently focused on clearing roads surrounding the park to allow the easy flow of morning commuter traffic.
Police observers say clearing the roads will also ensure police have full latitude of mobility for officers and vehicles if they do decide to clear the park.
LA Mayor Antonio Villaraigosa said he hoped for a "spirit of cooperation" with those camped out, adding he hoped police could clear the protesters out without violent clashes erupted.
Villaraigosa, who sought the court order police are now enforcing, however, did stress the park would eventually be cleared.
"As I said last Friday," the mayor said, " it is time for Occupy LA to move from focusing their efforts on this particular piece of parkland."