Unlike the original portable music player, Sony's latest must-have gadget does not arrive on virgin territory. Sector leader Nintendo has had the hand-held games market to itself for years.

But Sony is confident that the music and video capabilities of the PlayStation Portable (PSP), which first came out in Japan in December, will give it the edge.

Some branches of the Best Buy electronics chain opened their doors at midnight for the North American launch of the svelte black device.

Generally, however, stores reported brisk but not overwhelming sales of the 250-dollar PSP.

"Sales aren't quite as high as we were expecting for a new video system. We were expecting a line outside this store this morning but there wasn't," the manager of Circuit City in Arlington, Virginia told AFP.

"For the general public, the problem is the price: it's almost twice the price of a regular console," he said, declining to be named.

The manager at Gamestop in downtown Washington said first-day sales had been solid. "But we haven't had people beating down the doors," she added.

Sony has high hopes that the PSP will mark an important milestone towards its vision of a world hooked on integrated devices capable of doing much more than just play computer games.

It says the machine packs nearly the same amount of processing power as the PlayStation2 itself billed as more than just a games console, coming equipped with a DVD player and Internet capability.

"As the tremendous response to PSP continues to grow, we are redefining the marketplace with a comprehensive portable entertainment system," said Kaz Hirai, chief executive of Sony Computer Entertainment America.

Sony is the leader in home video-game machines with its PlayStation series. Gameboy maker Nintendo however remains by far the king among portables.

Nintendo released the DS, a hand-held console with a touch-sensitive double-screen, in both the United States and Japan late last year in time for the holiday retail rush.

It has already sold some two million units, with a goal of five million sold by the end of March.

Sony reportedly put back the European launch of the PSP to make more units available in the lucrative US market. It is offering the first million US buyers copies of the "Spiderman 2" movie.

The PSP plays games and movies on a new medium called Universal Media Disc, a mini-version of a regular compact or computer disc.

Sony has been criticised for its decision to go with yet another format in a media market that is already crowded with competing ways of watching films or listening to music.

It has also received brickbats for selling the device with just a 32-megabyte Memory Stick, hardly enough to store the contents of one audio CD.

In comparison, Apple's best-selling iPod music player -- one of the rival media that Sony has in its sights -- retails with up to 60 gigabytes of built-in memory.

Sony plans to release a four gigabyte Memory Stick for the PSP by the end of the month in the United States, but the cost will approach a whopping 1,000 dollars.