Around 5 a.m. police gave protesters 10 minutes to disperse their encampments. About 200 Protesters were seen chanting, with some wearing gas masks in preparation of possible tear gas.
In response, authorities arrested dozens of demonstrators and cleared out tents from the downtown plaza.
City officials warned protesters for the third time in three days that they do not have the right to camp in the plaza in front of City Hall and would face immediate arrest.
Altercations between Oakland demonstrators and police have been violent in the past, including a deadly shooting on Thursday near the encampment site.
Protesters had said that there was no connection between the shooting and the camp. But police Sunday night identified the slain man as 25-year-old Kayode Ola Foster of Oakland, saying his family confirmed he had been staying at the plaza.
An Iraq veteran also suffered a serious head injury during a police raid on the encampment. He's been released from the hospital.
Oakland is just one of the places where there have been clashes at the encampments.
Officials across the country have been urging an end to similar gatherings in the wake of three deaths in different cities, including the shooting in Oakland.
On Sunday, police drove hundreds of anti-Wall Street demonstrators from weeks-old encampments in Portland, arresting more than 50 people.
One man was taken away on a stretcher; he was alert and talking to paramedics. Officials said that one officer suffered minor injuries.
In other cities over the weekend:
- In Salt Lake City, police arrested 19 people Saturday when protesters refused to leave a park a day after a man was found dead inside his tent at the encampment.
- In Albany, N.Y., police arrested 24 Occupy Albany protesters after they defied an 11 p.m. curfew in a state-owned park.
- In Denver, authorities arrested four people as they forced protesters to leave a downtown encampment.
- In San Francisco, police said two demonstrators attacked two police officers in separate incidents during a march, leaving them with minor injuries. The assailants couldn't be located.
The Associated Press contributed to this story.