Amazon.com on Wednesday said the new generation Kindle electronic book reader is a best seller, with people snapping up the devices at a record pace.

While Amazon does not release Kindle sales specifics, it said that orders for the latest models of its device in the first four weeks have eclipsed those seen by other versions, "making the new Kindles the fastest-selling ever."

Amazon unveiled two new versions of its Kindle electronic reader in late July, including one that sells for 139 dollars, its lowest price yet.

The 139-dollar Kindle Wi-Fi connects to the online Kindle store by wireless only instead of 3G cellular networks like the previous Kindles.

Amazon said it began shipping the new Kindle models on Wednesday, two days ahead of schedule.

The Kindles weigh about 15 percent less and are 21 percent smaller than their predecessors, according to the California-based Internet retail giant.

"Kindle is the best-selling product on Amazon.com for two years running and our new generation Kindles are continuing that momentum," said Amazon senior vice president Steven Kessel.

Amazon founder Jeff Bezos has touted the new generation Kindle as "smaller, lighter, and faster, with 50 percent better contrast."

Amazon cut the price of the Kindle and revamped the line in the face of a threat in the e-reader market from Apple's iPad and companies like Sony and bookstore Barnes & Noble, which also offer e-readers.

Apple's cheapest iPad costs 499 dollars and features a color e-reader, compared with the black-and-white Kindle, which is devoted exclusively to digital books.

Barnes & Noble sells a version of its e-reader, the Nook, for 149 dollars while Sony's cheapest e-reader is 150 dollars.

Amazon's also offers a large-screen model, the Kindle DX, which costs 379 dollars.

Amazon said the new Kindles offer up to one month of battery life and double the storage to 3,500 books.