Amazon.com on Monday began shipping its Kindle 2 e-book reader a day earlier than originally planned.

Amazon said Monday that Kindle 2, introduced two weeks ago for preordering, is already the number-one seller on its Electronics Web site. Amazon unveiled the second version of the Kindle on Feb. 6 at an event in New York that featured Amazon Chairman, CEO and founder Jeff Bezos and best-selling fiction writer Stephen King, who wrote a novella called "Ur" exclusively for the Kindle to mark the launch.

The first version of the Kindle had been out of stock since November, its sales bolstered by an October endorsement from U.S. talk-show host and media mogul Oprah Winfrey. Amazon originally unveiled the Kindle in November 2007. With the Kindle, Amazon hopes to change the publishing industry and the way people read books the same way Apple changed the music industry and the way people listen to music with the iPod.

Kindle 2 costs US$359, the same price as the first version, but Amazon has made changes to it to make it more user-friendly.

Kindle 2 is slimmer than its predecessor and features 3G wireless for faster e-book downloads. It also has 2GB of memory, which allows it to store more than 1,500 books, whereas the original Kindle could store only 200 books. The battery life also is 25 percent longer than the previous version.

Other enhancements to Kindle 2 are a text-to-speech feature that allows the device to read aloud to users and a built-in 250,000-word dictionary so users can automatically look up words using a five-way navigational button with which the new device is equipped.