The larger 42mm (1.7in) models of the Watch will cost about $50 more than than the 38mm (1.5in) versions in the lower-priced ranges.

Apple also revealed that the devices are due to go on sale on 24 April.

Rivals' smartwatches have only seen limited sales to date.

A press event held in San Francisco held few surprises about the wearable tech beyond the fact that the mid-range stainless steel edition would start at $549 and go up to $1,099 in the US, and from £479 to £949 in the UK including VAT.

There had been speculation that Apple would seek a bigger price gap between the model and the basic aluminium-based Sport-branded version - something that would have restricted its appeal.

"Apple's pricing demonstrates the confidence it has in the new Apple Watch's functionality, design and consumer appeal," commented Ian Fogg from the consultants IHS.

Apple's website lists a total of 38 models, which might pose a challenge to how it markets them.

Apple's chief executive Tim Cook said the Watch would typically last owners 18 hours between charges, providing a day's worth of use.

Its website adds that the models take 2.5 hours to charge from 0% to 100%, and that the larger model has longer battery life.

It also reveals that a Power Reserve facility means that the Watch should continue to show the time for "up to 72 hours" after other functions are turned off.

The firm said on stage that thousands of new apps had already been developed for the Watch ahead of it going on sale.

The social networks Facebook and Instagram, the car pick-up service Uber and the Chinese messaging app WeChat are among those confirmed to have developed software for the device.

Apple also highlighted that its wrist-worn device could be used to make touchless payments and receive phone calls.

Other functions demonstrated by Apple included:

using the Watch as a means to open a compatible hotel room lock as an alternative to a key card
checking the name of a song via the app Shazam
opening an internet-connected garage door remotely
To provide many of its functions - including GPS tracking, receiving phone calls and transmitting messages - the Watch requires its owner to have an iPhone 5 or more recent Apple handset, limiting its potential audience.

CCS Insight forecasts 20 million units will be sold by the end of this year - representing about 7% of the compatible iPhones currently in use.

However, other analysts range widely in their predictions, forecasting sales as low as eight million units to as high as 60 million in 2015.

For comparison's sake, the iPad sold 14.8 million units in the first nine months after its launch, more than double Wall Street's most optimistic estimate.

The UK, US, France, Germany, Japan, Australia and Canada are among the first wave of countries where the smartwatches will be sold.

-BBC