Blizzard Entertainment said today that the expansion pack to its highly popular World of Warcraft online game sold nearly 2.4 million copies on the first day, becoming the fastest selling PC game ever.

On Tuesday the Irvine Calif.-based software firm said that The Burning Crusade add-on sold 1.2 million copies in North America, while 1.1 million boxes were sold in Europe on the first day.

The Burning Crusade has already exceeded even our most ambitious expectations, said Mike Morhaime, president and cofounder of Blizzard Entertainment. We're pleased that so many players are eager to see all of the new content that the expansion has to offer, and we look forward to seeing everyone online as additional players continue to upgrade in the days ahead.

World of Warcraft is the world's most successful massively multiplayer online game (MMORPG) with more than eight million players. Users pay up to $15 a month to gather with thousands of other real people in a never-ending fantasy world.

Blizzard said that it had supplied over 4 million copies to retailers worldwide. The game retails for $39.99 in the US.