Apple has unveiled three new iPhone models, including a top-of-line handset described as "the biggest leap forward" since the original iPhone 10 years ago.

Apple chief executive Tim Cook announced the premium iPhone X - pronounced ‘ten’ - as well as a new iPhone 8 and 8 Plus.

Mr Cook, speaking at the first event at the new campus theatre named for the late Apple co-founder Steve Jobs, said the latest flagship handset is a milestone for the company a decade after the first iPhone release.

"Ten years later it is only fitting that we are here in this place, on this day to reveal a product that will set the path for technology for the next decade," Cook said, calling the iPhone X "the biggest leap forward since the original iPhone."

The iPhone X has an edge-to-edge screen and uses facial recognition to unlock the device, and improved "super retina" display with improved graphics and resolution.

Apple senior vice president Phil Schiller said the glass-body iPhone 8 and 8 Plus handsets were the first smartphones "really created for augmented reality," with improved power and graphics over their predecessors.

Apple also unveiled an updated smartwatch and an upgraded streaming video system for 4K high-definition television.

The Apple Watch Series 3 has its own mobile connectivity which allows the user to remain connected without a smartphone for phone calls, music and other functions.

"The Apple Watch is now the number one watch in the world," Mr Cook told the media event.

While Apple has not provided detailed sales figures for the watch, Cook said sales were up 50% in the past quarter from a year earlier.

Apple said the new smartwatch offers several improvements including cellular connectivity and applications to help detect health problems such as heart arrythmia.

Around four out of five of the consumers who in the past bought the top end model would likely be willing to do so again despite the price jump, estimated analyst and veteran Apple watcher Gene Munster of Loup Ventures. 

Beyond that, Apple is expected to cover other price points by retaining some sort of low-end model similar to the current iPhone SE, which sells for $399. 

That is likely to ensure iPhone customers stay within the Apple ecosystem even if prices on top-end models rise.

Another factor for US sales will be discounts from carriers, which might opt to use the buzz around the new iPhone launch to lure customers away from their competitors by offering deals that would soften the blow of higher prices.