Carrey turned on the lights along Oxford Street while Colin Firth performed the honors at Regent Street.

British actor Bob Hoskins did the honors at St Paul's Cathedral.

All three later on Tuesday attended the world premiere in central London of filmmaker Robert Zemeckis' animated adaptation of Charles Dickens' classic A Christmas Carol, which features their voices.

Carrey, who voices the stingy character Scrooge in the new movie, said: "It feels great to be a part of all this tradition.

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"I want to thank the people of Britain for the legacy of Charles Dickens and the chance to tell this story. This story couldn't be more important now - it's about the immorality of greed."

After the lights were flicked on, tenor Andrea Bocelli at Leicester Square and the St Paul's Cathedral choir on the steps of the historic church led crowds in an attempt to stage the world's biggest carol singing event.

With large video screens at all four sites, organizers were hoping to draw large crowds for the coordinated singalong.

Carrey told Sky News the singing was "beautiful."

Asked what he thought of the Christmas decorations, Firth said: "Well I think it's all a bit tacky and over the top quite frankly, but why not? That's what Christmas is all about." AGENCE FRANCE-PRESSE