Apple iPhone 6 - and iWatch - due to be unveiled today

'iPhone day' expected to include two iPhone screen sizes, new iPads and an iWatch, according to rumours

Apple's latest smartphone, as well as a "smart watch", are expected to be unveiled by CEO Tim Cook tonight in a launch that has seen the company's share price ramp up in anticipation.

The new iPhone is expected to be slimmer than current models and to incorporate near-field communication (NFC) technology, enabling the popular device to be used for making touch-payments.

According to reports, the new iPhone will be offered with two different screen sizes - 4.7-inches and 5.5-inches - in a bid to attract custom from buyers looking at larger smartphones. They will also have a larger storage option of 128GB.

At the heart of the new iPhone will be a 2GHz Apple A8 64-bit microprocessor, based on underlying ARM intellectual property. Reports suggest that the A8 will have a large cache and also a "secure enclave" to store credit card data, which will work in conjunction with the NFC features.

Indeed, Visa, MasterCard and American Express have all signed up to a mobile payments initiative from Apple that may form part of a lucrative new revenue stream for the company - claiming a micro-share every time a user makes a payment with their new iPhone.

While the 4.7-inch iPhone 6 is expected to have a disappointingly small 1,800 mAh battery, the 5.5-inch model will have a larger 2,900 mAh battery - this alone will make it highly attractive given the frequent battery life complaints of many smartphone users.

A wilder rumour, perhaps, is that the new iPhone will have a tough sapphire screen cover to protect the screen against scratches and cracks.

Finally, the built-in camera is expected to be a 13-megapixel model supplied by Sony and the device in the US market will weigh in at around $700 unlocked.

Apple is also expected to unveil a refreshed range of iPads, which is expected to include a big 12- or 13-inch screen device as part of a plan to re-ignite sales that have started to flatten.

Perhaps most intriguing of all, though, are reports that Cook will also model and unveil the new iWatch, a wearable device that will have communication functions built-in. It is also believed that the iWatch will include health monitoring functions. Early "smart watches" had to be used in conjunction with a related smartphone over a Bluetooth connection for them to benefit from all the communications capabilities.

Production of all the new devices has been taking place all summer in a bid to ensure that strong early demand is satisfied, as well as sales during the crucial holiday period.

The launch comes at a time when Apple's declining market share figures outside North America are beginning to show, with the company's devices costing an average of around £500 compared to the sub-£100 starting price for well-regarded Android smartphones, such as the Motorola Moto-G.

Android devices are also selling in considerably greater volume in emerging markets, where sales growth is fastest.

However, Apple may spring a surprise by unveiling a more competitive iPhone offering - although such hopes were dashed last year when the iPhone 5c proved to be more expensive than expected.