The game’s global popularity and addictive nature has naturally lead to comparisons with Pokemon Go, which had teenagers glued to their smartphones as it achieved all-time high downloads of 750 million.
Industry experts doubt that Fornite: Battle Royale will achieve anything like that number.
But its success has been staggering, especially as it can only be downloaded by signing up for an invite.
Fortnite, which has topped the UK and US iTunes charts, started-out as a PC and console-only game where it was dubbed the “Call of Duty” for kids.
One hundred users have to shoot each other in a last man standing contest, but its offbeat humour and cartoonish visuals mean it does not depict extreme violence or bloody scenes.
A study claimed Pokemon Go, where users had to walk the streets searching for Pokemon to catch, was responsible for $7.3bn (£5.4bn) in costs across the US in the 148 days after its release.
Pokemon Go researchers attributed much of that figure to accidents they believe were caused by the game, which they also claimed cost the lives of two people.
Fornite is free to download, and like Pokemon Go, seeks to make revenue through in-game purchases, where players can buy their characters different outfits and accessories.
Forbes contributor Paul Tassi believes Fortnite’s set-up means it could generate more revenue than its Pokemon counterpart.
He wrote: “Pokemon Go with its incubators and outfits and lucky eggs has been a terribly monetised game from the start.
“Yes it did a billion plus in revenue easily, but with how big it was, Niantic really only scratched the surface of monetisation, selling stuff that people didn’t want.”
James Batchelor of Gamesindustry.biz said: “Fortnite is the latest game to prove how powerful a free game offering can be.
“The impressive revenues Epic has generated show that people are more than willing to invest in an experience they enjoy.”
Fornite’s rapid success on the iPhone is unlikely to have suprised many in the gaming world, after the PC, Playstation and Xbox versions made a combined $126m (£89m) in revenue in February, according to research company SuperData.
Developers Epic Games are planning to make it available for Android.
Nick Chester, PR manager for Epic Games, said: “There’s a very wide range of Android devices that we want to support.
“We want to make sure Android players have a great experience, so we’re taking more time to get it right.”
The popularity of Fortnite is naturally stirring up anxiety amongst parents, with many reporting their child is “addicted” to the game.
US blogger Amy Selling’s post “how I lost my kids to Fortnite” went viral in February.
She received hundreds of messages from parents who had similar experiences, with one complaining that her son had “changed” since he started playing Fortnite.
It comes amid reports the World Health Organisation is set to include “gaming disorder” in its list of mental conditions in 2018.
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The WHO proposes to list it under “disorders due to substance use or addictive behaviours”.
The organisation’s description of the disorder says it is “characterised by a pattern of persistent or recurrent gaming behaviour”.