Oreo cookie celebrates its centenary in the US and four other countries, China, Saudi Arabia, Venezuela and Indonesia.

Flash mobs in seven US cities sang “Happy Birthday!” to the famous cookie: a white filling (or cream) sandwiched between two black biscuits.

The first Oreos were baked at the Nabisco factory in New York in 1912.

Oreo cookies are now sold around the world, bringing Kraft Foods – which owns Nabisco – $2 billion annually.

“It’s the best-selling cookie in the world,” said John Ghingo, senior director for Oreo Global at Kraft.

“The simple act of enjoying an Oreo cookie and glass of milk continues to speak to a universal, human truth: inside all of us… there’s a kid that deserves to be set free every once in a while,” John Ghingo said.

To mark the cookie’s centenary, Nabisco released a limited edition of "Birthday Cake" Oreo

John Ghingo added that the name Oreo remained mystery even today, but one theory suggested that the two uses of “O” in the word represented the cookies and the “re” in the middle stood for the cream.

To mark the milestone, Nabisco released a limited edition of “Birthday Cake” Oreo.

On Tuesday, celebrations were also held in China, Indonesia, Saudi Arabia and Venezuela.

 [youtube yb10oo0B8uE]