A free mobile game spun from blockbuster video game franchise "Fallout" has rocketed to the top of the charts at Apple's online App Store.
Bethesda Softworks on Thursday announced that "Fallout Shelter" became the most downloaded game in 48 countries, and the most downloaded application of any kind in 25 countries, shortly after its release last week.
"We play games on our phones all the time, and have always wanted to make one," Bethesda Game Studios director Todd Howard said in a release.
"To have our first mobile game be enjoyed by so many is stunning."'
"Fallout Shelter," which lets players make in-game purchases of virtual items, became the third top-grossing application at the App Store within two days of its release, according to US-based Bethesda.
"Fallout Shelter" was played more than 70 million times a day around the world in the week after its release on June 14, the company said.
The game is described by its creators as "a post-nuclear strategy and simulation experience that puts you in control of a state-of-the-art underground Vault" similar to fictional survival bunkers depicted in the video game franchise from which the application sprang.
Bethesda, a unit of ZeniMax Media, released the mobile game as it showed off a keenly awaited "Fallout 4" at the Electronic Entertainment Expo media event in Los Angeles.
"Fallout 4" opens with scenes showing a young family in a setting that blends 1950s America with the future.
Nuclear bomb blasts send people racing for shelter, and the main character becomes the sole survivor, emerging two centuries after the devastation.
A collector version of the game comes with a real-life Pip-Boy wrist-wear device, a gadget well-known by fans of "Fallout."
The wearable Pip-Boy is designed to hold smartphones, and there will be an application to make it an extension of the game, according to Howard.
"Fallout 4" will be released on November 10, with versions of the game tailored for play on Xbox One and PlayStation 4 consoles as well as on personal computers powered by Windows software.
The mobile application is only available for devices powered by Apple software.