Sales of electronic book readers are booming, companies are jostling for a share of the fledgling market and Amazon's going global with the Kindle.

So why is all the buzz about Apple?

Because the California company behind the Macintosh computer, iPhone and iPod is rumored to be coming out with a portable tablet computer early next year that may double as an e-reader.

And not just a black-and-white e-reader but one that would boast full colour and a 25-centimeter screen making it more of an oversized iPod Touch or a netbook computer, the increasingly popular low-cost mini-laptops.

If an Apple tablet computer does emerge, it would join an e-reader market that is becoming increasingly crowded but is undergoing tremendous growth.

Besides Amazon, other companies offering e-readers include Japan's Sony, Britain's Interead, and Dutch company IREX Technologies, whose touchscreen reader with wireless capability is expected in US stores in October.

Barnes and Noble, the book giant, is among those expected to throw down the gauntlet to market leader Amazon next along with Plastic Logic, maker of a lightweight large-screen device geared towards newspaper and magazines.

Forrester Research, Inc., in a report released on Wednesday, estimated that three million e-readers would be sold in the United States this year, up from a previous forecast of two million units.

Forrester said it expected 900 000 units to be sold in the upcoming holiday season alone and for e-reader sales to double to six million units next year, bringing cumulative sales to 10 million units.

"We've been saying for some time now that this Christmas is going to be 'e-reader Christmas,'" Neil Jones, founder and chief executive of Interead, maker of the COOL-ER e-reader, told AFP.

"Our biggest challenge as an industry is making sure we have stock available for people who want to buy an e-reader," Jones said, adding that COOL-ER sales have been "three to four times ahead of our predictions."

Amazon does not release Kindle sales figures but Forrester estimated the online retail giant has a nearly 60 percent share of the US market followed by the Sony Reader with 35 percent.

Seattle-based Amazon has also finally begun looking beyond US shores, unveiling an international version of the Kindle this week designed to synch with wireless networks in 100 countries around the world.