Free-to-play card-combat phenomenon Hearthstone: Heroes of Warcraft has been downloaded upwards of 20 million times, Blizzard has announced.

"Thank you all for joining us in Hearthstone! We're going to need a bigger tavern!" the developer stated on Twitter above the following image noting the milestone.

Hearthstone launched on PC and Mac back in March then appeared on iPad in April and Windows 8 Touch devices in August. It's slated for release later this year on iPhone and Android.

Earlier this month Blizzard released its single-player expansion The Curse of Naxxramas, which our Tom Bramwell said "seems well worth owning" in his review. "The solo content has its ups and downs, but it is most often fun, and also offers some welcome environmental refreshment."