Much speculation has centred on the mystery gadget being a notebook-sized device using a similar touchscreen interface and operating system as the iPhone and iPod Touch.

It would be targeted as a platform for online publications, and has been touted by some as a possible saviour for the struggling US newspaper industry.

Paid content

In recent years Apple has emerged as an industry leader in conditioning consumers to pay for digital content such as applications, music and games.

Analysts say the tablet device could herald a similar path for struggling "print" publishers, as a platform for consumers to browse and buy compelling multimedia content.

Speculation has centred on the new device building on the success of the iPhone [AFP]
On Tuesday speculation about the highly-anticipated device intensified further following comments by the CEO of US publishing group McGraw-Hill.

Appearing on US business network CNBC, Harold McGraw was asked about the rumoured tablet, responding that company officials would "make their announcement tomorrow [Wednesday] on this one".

He said: "The tablet is going to be based on the iPhone operating system."

The brief comments, which sounded authoritative, immediately sent the tech world into overdrive, with Twitter registering dozens of tweets every minute on the term "Apple tablet".

McGraw-Hill is a major developer and publisher of educational materials and textbooks, with several of its college texts already available for download on Apple's iPhone.

If the tablet device is based on the iPhone system, the investments McGraw-Hill and other publishers have already made in e-books would still be relevant on the new device.