Apple has unveiled a top-of-the-range tablet called the iPad Air that is 20% thinner than the previous version.

The 9.7in (24.6cm) computer is 7.5mm (0.3in) thick and weighs 1lb (469g), which the firm claims is the lightest full-sized tablet on the market.

It is powered by the same A7 chip found in the company's iPhone 5S.

The launch comes at a time when some analysts have suggested that Google's Android is about to overtake Apple's iOS as the bestselling tablet platform.

Apple also announced a new version of its iPad Mini.

Its 7.9in (20cm) screen has been upgraded to feature 2048 by 1536 pixels - the same as the larger model. It is being branded as 'retina' to highlight the increased resolution.

Amazon and Google have already announced small tablets - the Kindle Fire HDX and Nexus 7 - with similar high definition displays.

'We've got the retina upgrade to the smaller iPad that many thought should have been there in the first place,' Tony Cripps, principal analyst at tech consultants Ovum, reflected after the announcement in San Francisco.

iPad Mini
The iPad Mini's new screen has 326 pixels per inch, similar to the 323ppi resolution of the Nexus 7
'Market share slip is inevitable because so many rival devices are coming out, which is not necessarily a bad thing as the overall sector is growing..