Google Music – the search giant’s long-awaited rival to Apple’s iTunes, Amazon, Spotify and others – was fully-launched last night after six months in beta mode. Google used a special event in Los Angeles to announce that the service would launch in sync with a new music store on the Android Market, offering a library of some 13 million songs from three of the big four record labels plus 1,000 "prominent" independent labels.

“You can purchase individual songs or entire albums right from your computer or your Android device and they’ll be added instantly to your Google Music library, and accessible anywhere,” said Google in an official blog post.

It has struck deals with Sony, Universal and EMI but not Warner Music. Sources at Bloomberg said this was because “pricing and piracy concerns” have not yet been resolved.

While Android – now the most popular smartphone platform – presents Google with a huge addressable market, experts believe that Google may struggle to challenge the dominance of iTunes, which was launched way back in 2003 (four years prior to the iPhone). The store generated US$1.5 billion in revenue for Apple in its most recent quarter.

“They’re coming into this market rather late in the game, where there are large, established players,” Gartner analyst Ray Valdes told Bloomberg. “You can say it’s a saturated market.”

“They have to overcome the No. 1 incumbent in this area,” added Ovum analyst Mark Little. “That’s not an easy company to grab share from.”

To kickstart the service, Google says it is “celebrating our launch with a variety of music that you won’t find anywhere else, much of it free.” This includes music from the likes of the Rolling Stones, Coldplay, Busta Rhymes, Shakira and Pearl Jam.