The actress's close friends' made 23 paper models representing each year of the birthday girl's life, reported Sun online.
"Emma was gobsmacked when she arrived at the party to see all the pinatas. There was everything from her as a child, and as Hermione in the Harry Potter films, to her in the Chanel advert a couple of years ago," said a source.
"They had even gone to the effort of stuffing a few of the pinatas with sweets and treats, so Emma could smash them open," the source added.