Anti-capitalist protesters claim they have "fulfilled" a goal after moving into Paternoster Square, home to the London Stock Exchange.
Activists, who were prevented from occupying the area in October, said 50 people accessed the square with tents and supplies at around 7pm on Tuesday.
An Occupy London spokesman said their successful arrival proved their movement was a "force that will not be stopped".
The site is just yards from St Paul's Cathedral where demonstrators dug in for four-and-a-half months after their first bid to pitch tents on Paternoster Square was derailed by police.
"This was something we have wanted to do on October 15 and we have finally done it," the spokesman added. "Even if we lose it tonight, it proves that we can do it. This is what it's about. This is a force that will not be stopped."
Activists were unable to say how long they expected to remain on the square.
"There's an injunction at Paternoster Square so they are waiting for a while," the spokesman added. "We don't know what's going to happen but we have fulfilled a medium term goal which is of course rather satisfying."
Earlier, members of the Occupy group handed out thousands of flowers to passengers at London's Liverpool Street station, bearing the message: "There Is Something Better Out There" during a day of rallies and marches across the country.
Their camp outside St Paul's forced it to close for a week in late October for the first time since the Second World War.
It also led to the resignation of the cathedral's Canon Chancellor Dr Giles Fraser and then Dean of St Paul's, the Rt Rev Graeme Knowles.