After more than a year of missteps by Apple Inc.'s tablet rivals, at least one viable competitor appears to have surfaced for the popular iPad.

Amazon.com Inc. on Monday trumpeted the success of its recently launched Kindle Fire tablet, part of a family of Kindle products that include low-priced e-readers. The company said it sold more than four times as many Kindle products on Black Friday last week as the same shopping day in 2010.

The Seattle-based online retailer declined to provide precise figures, other than to say it had sold 'millions' of its recently released Kindle tablets and e-readers even before the holiday shopping week, adding that the Fire, released this month and the first Kindle product with a color screen, has been its best-selling item for eight weeks.

As many as five million of the $199 Kindle Fires could be sold by the end of January, analysts at Forrester Research estimate, easily cementing the device as the second-place competitor to the iPad. About 13.5 million iPads are likely to be sold during the holiday quarter, estimated Gene Munster, an analyst with Piper Jaffray.

Another device that evolved from the e-reader market, the $249 Nook Tablet from Barnes & Noble Inc., also appears to be generating customer interest, said Sarah Rotman Epps, an analyst with Forrester Research. She believes the showing of the two companies suggests the tablet market has room for more than one strong brand.

'Today, the tablet market resembles the MP3-player market,' Ms. Epps said, a reference to the fact that Apple's iPod has controlled roughly three-quarters of the market for digital-music players for years. 'With Amazon and Barnes & Noble, you have brands that can be competitive,' if on a smaller scale than Apple.

Jamie Iannone, the head of digital products at Barnes & Noble, said he believes customers are attracted to the company's books, apps and movies. 'It's not about being inexpensive, it's about value,' he said.

Apple declined to comment.