LONDON - Jim Carrey and other Hollywood stars switched on the Christmas lights in London on Tuesday as part of festivities that included an attempt to stage the world's biggest carol sing-along.

Carrey turned on the lights along Oxford Street while Colin Firth performed the honours at Regent Street, two of London's main shopping strips.

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

All three later attended the world premiere in central London of filmmaker Robert Zemeckis's animated adaptation of Charles Dickens's classic "A Christmas Carole," 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.

"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, organisers were hoping to draw large crowds for the coordinated singalong.

Carrey, sporting a long, bushy beard, 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."