The move came a day after the dean of St. Paul's said the 300-year-old cathedral would close to visitors for the first time since World War II because the camp outside its main entrance is a safety hazard.
Protesters quietly put up 30 tents in Finsbury Square, The Guardian reported. A group then marched from St. Paul's, less than a mile away, and announced a "general assembly."
The protest at St. Paul's, using the name Occupy the London Stock Exchange, began last weekend. The group originally intended to camp in Paternoster Square, where the stock exchange is located, but were blocked by police from the privately owned area.
Organizers said the Finsbury Square camp is an addition to the St. Paul's one, which was becoming overcrowded as more people join the movement.
Some of those camped at the cathedral promised to stay until Christmas, while others said they will still be in the area next summer when the 2012 Olympics will be held in London.
"I'll be here next summer if that's what it takes to change the system," said David Harris, 36, a former army infantryman from the Liverpool area.
The movement began last month in New York as Occupy Wall Street and has spread around the United States and to other countries.