Police and bailiffs began dismantling Occupy London's campsite outside St. Paul's Cathedral late Monday.
The protesters said vans loaded with police arrived at the site before midnight.
The local authority, the City of London Corporation, confirmed the eviction was under way by bailiffs, backed by police, and asked the protesters to move on peacefully.
Civic authorities have an eviction order allowing them to remove the activists' tents, though not the protesters themselves.
As the eviction began, some protesters attempted to wear their tents as clothing and others used wooden pallets to form barricades. There were no immediate reports of arrests.
Protesters against capitalist excess inspired by New York's Occupy Wall Street movement have been camped outside the 300-year-old church since October.
They say they are exercising freedom of speech and drawing attention to a warped capitalist system that spawned a global financial crisis.
Local authorities claim the camp has harmed nearby businesses, caused waste and hygiene problems and attracted crime and disorder.
Last week, a court rejected the protesters' challenge to the eviction order, ruling that the right to protest did not justify a semi-permanent camp on a public pathway.
By Monday night there appeared to be several dozen protesters at the site, down from hundreds at the height of the camp.
Occupy London: http://occupylsx.org/
City of London Corporation: http://www.cityoflondon.gov.uk/Corporation