Sony Corp shifted 321,400 units of the PlayStation Vita, its new handheld game device, in Japan in its first two days on sale, research firm Enterbrain said on Tuesday.

That falls short of rival Nintendo Co Ltd's 3DS, which sold 371,000 in its first two days, Enterbrain said. Sales of the 3DS, however, slumped weeks after the launch, forcing Nintendo to slash the price and crushing its profit outlook for the year.

Sony seeks to avoid suffering a similar fate by offering a big slate of 24 games for the Vita at launch. But executives admit the real challenge will come in maintaining sales over the next few years.

Fans in Japan lined up to be among the first to pick up the latest portable game device, which kicked off a global rollout on Saturday. The Vita will be launched in the United States and Europe in February.

Sony's previous portable game device, the PS Portable, sold 166,000 units on the first day of sales in 2004. It has sold 73 million units to date.

(Reporting by Isabel Reynolds; Editing by Chris Gallagher)