Amazon.com unveiled larger, faster, aggressively-priced Kindle Fire tablets on Thursday, challenging Apple’s dominant iPad and intensifying a battle with Google and Microsoft in the booming tablet arena.

Amazon’s CEO unveiled the Kindle Fire HD and also showed off a "paperwhite" e-reader with a much sharper screen and longer battery life.

Amazon is willing to make little or no money selling cheap tablets and e-readers because it wants to get the devices into as many hands as possible, then sell higher-margin digital content, such as e-books, video, games, apps and music, to a more connected and engaged customer base. Shares in Amazon Thursday closed on the Nasdaq up 2.1 percent at $251.38, after hitting an all-time high of $252.70 during the session.