Hundreds of people stared into the skies above London as a glowing disc appeared over Tower Bridge to mark the launch of the latest instalment of the Halo computer game franchise.
The Halo logo was suspended from a helicopter and flown over the capital's biggest landmarks as the Xbox 360 title went on sale.
The Halo franchise has already sold 46 million copies and the previous version made a total of \$200m (£124m) in the first 24 hours following its launch.
Microsoft hopes the return of Master Chief, the laconic green-armoured super-soldier protagonist of Halo, after a five-year hiatus will bring gamers out in droves.
Halo 4, which was launched simultaneously in 40 countries, is expected to outdo the box office takings of James Bond film Skyfall this weekend.
The Halo series, made by Microsoft Game Studios, spearheaded the company's foray into gaming that began with the 2001 launch of the first Xbox console.
The Halo games, originally developed by Bungie, have been fundamental in giving the console a market lead over Sony's PlayStation and Nintendo's Wii and has generated revenues of \$3bn.
However, it remains to be seen if the well-reviewed game can revive flagging video game sales or surpass Call Of Duty: Black Ops II, which goes on sale next week and is likely to vie for the title of 2012's top-selling game.
"Because there hasn't been a game to star Master Chief for five years, there's a bit of a pent-up demand," said Ryan McCaffrey of videogame website IGN.com.
"Call Of Duty has taken over as the most popular game on the Xbox, so I think it will be very close."
In Halo 4, Master Chief deals out death and destruction to evil aliens while embarking on a quest to save his longtime friend and artificial-intelligence construct Cortana.