Produced by Westfield London's in-house event team the diva drew the biggest crowd ever seen at the mall for an event.
Thousands of fans, who had been queuing for hours outside the Shepherds Bush-based shopping centre, packed the venue to its rafters.
Keeping the crowd waiting the songstress finally made her entrance some 30 minutes behind schedule and the crowd went wild screaming as she made her way to the stage.
After addressing the crowd and telling them that it was the first time she had ever been in a shopping centre, she gave an impromptu verse of her hit single All I Want For Christmas.
Westfield London event manager Joe Russell said: "Mariah Carey switching on the Christmas lights at Westfield London was the perfect culmination of a hugely successful year for the centre and was one more step in helping to establish The Atrium as London's newest venue."
Carey will next be on ITV on Sunday night (22 Nov) as part of the X-Factor live finals.
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