Apple has introduced the new fourth generation iPod nano, the thinnest iPod ever featuring a sleek new design with a curved aluminum and glass enclosure, in nine colors.

The new iPod nano incorporates Apple’s Genius technology which automatically creates playlists from songs in your music library, with just one click.

The new iPod nano also features a refined user interface, a high resolution portrait display and a built-in accelerometer which automatically switches to Cover Flow when rotated and automatically goes into Shuffle mode when lightly shaken. The new iPod nano gives users up to 24 hours of music playback or four hours of video playback and is available worldwide immediately in 8GB and 16GB models.

Both models come in silver, purple, blue, green, orange, yellow, pink, (PRODUCT) RED and black.

“The iPod nano is the world’s most popular music player and we’ve made it even better for this holiday season,” said Steve Jobs, Apple’s CEO. “We think users are going to love the amazing new design, the automatic Genius playlist creation, as well as automatically going into Cover Flow with just a turn of the wrist.”

iPod nano works seamlessly with iTunes so users can import, manage and then auto-sync their favorite content. You can buy music, video and games for your iPod nano from the iTunes Store with more than 8.5 million songs available for preview and one-click purchase.

The 16GB model holds up to 4,000 songs, 14,000 photos and 16 hours of video, and the 8GB model holds up to 2,000 songs, 7,000 photos and eight hours of video.

The new iPod nano works with the new iTunes 8 Genius feature, allowing customers to automatically create playlists while on-the-go with their iPod nano. Users can preview the playlist Genius creates, refresh the list to choose different songs and save Genius playlists to enjoy again later.