The new iPhone 6s and 6s Plus models have been launched, with record sales expected.
Analysts predict that Apple could sell 12 to 13 million devices in the first weekend alone, a rise from 10 million in sales for the previous model.
With Apple announcing the next generation of iPhones on 10 September, fans have already been queuing up around the world days before release to be the first customers for the new device.
Sales of the smartphone accounted for nearly two-thirds of Apple's revenue in the latest quarter, making it the company’s best-selling device to date.
"The stage is set for Apple to show year-over-year growth over the Herculean iPhone 6 sales," FBR Capital Markets senior analyst Daniel Ives said.
After a major external redesign last year, which included a larger screen and the addition of mobile payments, this generation’s improvements are less immediately noticeable.
The new models, which are the same size as last year, feature improved cameras and 3D touch, a display technology based on a 'Taptic Engine' that responds according to how hard users press their screens.
Repair firm iFixit, which has already dismantled the 6s to investigate its internal components, said the size of the battery had been reduced from the iPhone 6 and speculated that this was to accommodate the Taptic Engine.
Despite the physical downgrade, Apple has said that the new model maintains the same battery life as last year.
The new iPhones also use chips made by Qualcomm, Avago Technologies, Qorvo Inc's TriQuint Semiconductor and RF Micro Devices, Toshiba, Texas Instruments and Skyworks Solutions, among others.
Analyst Patrick Moorhead of Moor Insights & Strategy said that Apple could make some major headway against Samsung with the 6s due to lacklustre performance of the Galaxy S6.
"Over the long haul, the 6s will eclipse the 6 as Apple is even more competitive versus Samsung in emerging regions and is gaining share in traditional regions," he said.
"Samsung didn't bring a whole lot of compelling features to consumers with their new lines of phones."
One of the first customers to pick up the new model in Sydney, Lucy Kelly, sent a robot to queue for her two days in advance.
"I obviously have my work and other things to attend to and can't spend two days lining up so my boss at work suggested I take one of the robots down and use it to stand in my place," she said via an iPad mounted on top of the wheeled robot.
"I love new gadgets. The new camera is meant to be amazing."