The tech giant is said to have equipped the iPhone 5S with a 12 or 13-megapixel camera and is widely believed to have created a gold version of its handset.
It is expected to introduce the gadget during an event at its California headquarters where some rumours suggest it may reveal its first budget model, dubbed the iPhone 5C.
The cheaper version of the iPhone will reportedly be produced in a range of vivid colours and would present an obvious rival to the low-cost handsets sold by Apple's major competitors.
A simultaneous event will be hosted by Apple in Berlin.
The Cupertino-based firm has remained as tight-lipped as ever in the run-up to the conference which comes at a time when it faces stiffer competition than ever before.
But supposed "leaked" images which claim to show the 5S have created a considerable stir online.
They appear to show a silver ring encircling the home button - thought to be part of the fingerprint sensor.
Motorola's decision to introduce a sensor in 2011 drew mixed reviews with some customers reportedly unable to access their phones when devices failed to identify their fingerprints.
If the rumours are true, Apple's next-generation device could go on sale next Friday and may closely resemble its predecessor from the outside.
Traditionally, the company has upgraded internal hardware for the "S" handsets but the exterior remains relatively untouched. This means the iPhone 5S could look very similar to the iPhone 5 but with a more powerful processor.
Tonight's event comes at a time when Apple is also expected to reveal its latest operating system - due for release in September.
Chief executive Tim Cook dubbed iOS7 the "biggest change to iOS since the introduction of the iPhone" when he announced the new softwear earlier this year.
The system has been designed to make the iPhone appear bigger, with features crafted to take advantage of the entire screen.
Ernest Doku, telecoms expert at comparison site uSwitch.com, said the event could be "one of the most exciting yet" from Apple and added: "a cheap and cheerful iPhone could be the silver bullet needed to halt Android's rise."
"The latest word is that two iPhones will make a simultaneous appearance - a premium sequel in the iPhone 5S, and a low-cost iPhone 5C," he said.
"While the iPhone 5S is tipped to arrive with a faster processor and improved camera, it's the cool iPhone 5C - rumoured to be available in an array of eye-catching colours - that is likely to garner all the attention.
"Much like the compact iPad mini lowered the barrier to entry and effectively introduced tablets to an entirely new demographic, a more affordable and attractive iPhone could attract the lucrative mid-range market in droves."
Jan Dawson, chief telecoms analyst at research firm Ovum, said targeting markets in countries such as China with a cheaper handset was key for Apple to drive growth.
"The cheaper iPhone is critical for expanding the addressable market, because many people in China and elsewhere simply can't afford to buy a current generation iPhone, especially when it's not subsidised," he said.
"However, the key risk for Apple in launching a cheaper iPhone is that it may cannibalize sales of the high-end phone... The trick is for Apple to position a cheaper device so that it's attractive for those that haven't been able to afford an iPhone before, but is missing enough key features for the new flagship iPhone to remain compelling."
Fred Huet, managing partner at management consultancy firm Greenwich Consulting, said the focus was now on Apple's future in China but warned the budget phone could have "serious repercussions on Apple's carefully managed image".
"As a brand that has always set itself apart from others by its innovation and by the quality and price of its products, this change of strategy could be Apple's undoing," he said.