Google Inc yesterday began selling digital books, intensifying the search engine's competition with Amazon.com Inc and Apple Inc and marking a significant push by the company to expand into the e-commerce business.

The new online bookstore, dubbed Google eBooks, features 3 million titles, from newly released best-sellers to freely available out-of-copyright books, which consumers can store in a personal online library managed by Google and then read on any device.

"All of your library is there at anytime; any device you pick up, all your books are present," James Crawford, the director of engineering on the Google Books team, told Reuters.

The electronic books market is currently dominated by Amazon.com, which helped establish the market with the release of its Kindle reading device in 2007 and has a roughly two-thirds share of the United States market, according to Forrester Research.

Earlier this year, Apple entered the market, selling electronic versions of books that can be read on its popular iPad tablet.

Google has an opportunity to offer electronic books to a vast segment of consumers who might not have been aware of electronic books, said Forrester Research analyst James McQuivey.

Google said its digital books are compatible with a number of reading devices, including the Barnes and Noble Nook and Sony e-reader, but are not compatible with the Kindle.

While Google's experience in e-commerce is limited, some analysts believe that the transactional revenue from selling electronic books may be less important to Google than the breadth of online services it will be able to provide by offering books.