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Blizzard has taken the wraps off the new video game it has been developing - a collectable card game.

Called Hearthstone: Heroes of Warcraft, the duelling game is based around cards players gather.

The game will be free to play in that people can earn cards by playing, but they will advance faster by buying cards in stores.

Blizzard said Hearthstone was going through internal testing but would be released before the end of 2013.

Cards in the game are based around characters, spells and artefacts from Blizzard's Warcraft world to make them immediately familiar to players, said Rob Pardo, Blizzard chief executive during a presentation about Hearthstone at the Pax East gaming convention. Packs of five cards would cost about $1 (60p) each, he said.

Cards bought in stores are replicated in the online game in which people duel with other players calling on weapons, spells and followers to help defeat an opponent.

Duplicate cards can be converted online into "arcane dust" that can be stockpiled and then used to craft the rare cards players need to do better in duels.

Currently, there is no direct connection between World of Warcraft and the Hearthstone game. However, people will need a Blizzard Battlenet account to play the card game. It will be playable on PCs, Macs and on Apple tablets.

Hearthstone could face competition from game studio Mojang which is developing a similar game called Scrolls. In addition, there are many other well-established collectable card video games such as Duel of the Planeswalkers.

Olivia Grace, a contributing editor at online gaming site Wow Insider, said the game was "definitely not" what she and other keen gamers were expecting,

"This is something of a surprise, yes, and it's not that remarkable that there have been feelings of disappointment," she told the ´óÏó´«Ã½.

Despite this, she said, Hearthstone looked well put together.

"The microtransaction-based free-to-play business model is a new endeavour for Blizzard, and hopefully they'll execute it well," she added. "Also, given the existence of the WoW Trading Card Game, it'll be interesting to see whether there's any incorporation of the TCG into this new one."