Los Angeles: Riot police arrested more than 60 anti-Wall Street protestors in San Diego while clearing a camp there, a spokesman said, in the latest clampdown on such demonstrations.

Officers arrested 51 people in Civic Center Plaza in downtown San Diego, where protestors had been camped out for the last three weeks, and another 11 at a nearby park, said police Officer David Stafford.

There were no reports of injuries in the operation, which started at 2:00 am and lasted 45 minutes, and came three days after riot police cracked down on a similar camp near San Francisco, leaving one person critically injured.

Over the last three weeks, San Diego police said they had received "numerous complaints from facility staff about the unsanitary conditions created by human and animal feces, urination, drug use, littering and damage to city property.

"We requested that all persons leave the Civic Center Plaza in order to allow a cleaning crew to conduct a thorough cleaning," added a San Diego Police Department statement.

On Tuesday, police in Oakland, near San Francisco, launched a dawn raid to break up an anti-Wall Street camp, arresting some 97 people.

Later that day officers fired tear gas and bean bags to disperse crowds who tried to return to the site of the camp in the evening, critically injuring one person, a former marine who had served two tours in Iraq.

The victim, Scott Olsen, is reported to be recovering in hospital.