Game maker Blizzard has announced that World of Warcraft has reached six million subscribers worldwide.

Blizzard's stunning MMORPG (massively multiplayer online role-playing game) has reached a frenzy that has even surprised officials at the Irvine, California-based developer.

"World of Warcraft's growth continues to exceed all our expectations," said company president Mike Morhaime.

"We want to reiterate our thanks to the millions of players worldwide and to all the retailers who have enthusiastically supported the game over the past year."

World of Warcraft was launched about a year ago in the US, Australia and New Zealand.

The adventure game has since been released in multiple countries throughout Europe and Asia.

Seeing the popularity, Blizzard announced last October that it would release an expansion pack later this year.

The expansion will add new lands, quests, monsters, magic items, spells and abilities, two new player races, a new player profession and 10 new levels of power for players to achieve.