Apple has unveiled a foldable phone called Duo, introducing the biggest change in years in the company's flagship product.
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The Duo is sized and shaped like a passport, with rounded edges.
It opens into a horizontal 19cm screen that also can be viewed vertically.
There is a smaller single screen on the front, when the phone is folded.
When open, it is Apple's thinnest phone, the company said.
The folding phone event, the first with new CEO John Ternus at the helm, is the most noticeable overhaul of Apple's flagship product since it removed the physical home button from the iPhone X in 2017.
The iPhone brought in $US209.6 billion ($A290.0 billion), or just over half of Apple's sales, in its most recent fiscal year.
Apple positioned the iPhone Duo as a business productivity device, showing how it would manage Zoom calls with multiple participants and a broader view of the Slack messaging app.
The Duo's larger screen will support multiple app windows at once, a move aimed at productivity that Apple has made with some of its iPads.
Ternus criticised existing foldables as awkward and poorly suited for common tasks such as scrolling and video viewing, saying the Duo was designed to deliver an iPad-like experience in a pocket-sized device through a custom hinge, dual displays with a consistent aspect ratio and a new titanium body.
"It's entirely new and at the same time remarkably familiar. A similar size to your passport, it feels familiar to hold and comfortable to use with one hand," Ternus said.
Apple said the iPhone Duo will feature the A20 chip to drive its displays and also a new C2 modem chip designed by Apple, part of its move away from Qualcomm's wireless data chips.
"Apple has created a new premium growth opportunity, opened up another revenue stream and injected fresh momentum into the iPhone business," PP Foresight analyst Paolo Pescatore said.
Apple's US shares were down 1.8 per cent at the end of the presentation.
Former chief executive Tim Cook handed over the leadership baton to Ternus at the start of the presentation with a video about how to start the event.
The video ended with a close-up of Cook, who said, "Not me. That's your guy," pointing back toward Ternus.
Ternus touted the iPhone platform as a personal AI hub that focused on privacy, saying that others wanted to collect and store personal data.
"Honestly, trust only goes so far when your data is no longer yours to control," he said.
"That's why Apple Intelligence runs on-device whenever it can."
Apple's Lilian Rincon, who oversees AI products for the iPhone maker and was recruited from Google earlier this year, described an updated Siri assistant that will work with 300,000 apps at release.
Executives also showed off the iPhone 18 Pro and the 18 Pro Max handsets that are the latest versions of Apple's well-known line, which do not fold.
Apple also unveiled a feature aimed at addressing growing concerns over AI-generated and manipulated images.
It introduced a new standard it calls "Apple Reference Image" to prove the authenticity of the images taken with the new iPhone 18 Pro cameras and said it will also support the emerging SynthID standard for identifying images that have been created or edited with AI.
The Apple Reference Image feature will not be available in European Union countries or China.
The iPhone 18 Pro will also include the new A20 Pro chip, which brings improvements to help advanced AI models to run directly on iPhones.
The company also said a new version of AirPods would come with noise cancellation, a first for its budget line of earbuds, and that a more expensive version would be available with extra features such as wireless charging and on-stem volume control that would allow users to adjust the volume by swiping up or down on the stem.
Apple also introduced the Apple Watch Series 12 and Apple Watch Ultra 4, positioning them as major health-focused upgrades.
That includes a redesigned sensor system that collects heart rate more frequently than before and powers new features that gauge recovery and fitness.
The company said the watches use new Apple silicon and improved sensors to deliver what it called the most accurate heart-rate tracking in a wearable.
Ternus previously served as Apple's hardware chief but has kept a low public profile aside from a handful of product introductions and sustainability initiatives.
It will fall to Ternus to persuade Apple's customers that they need a foldable device costing at least $A3499, a new high for a global brand that has defined mass luxury.
While Samsung Electronics and Huawei Technologies have sold folding phones since 2019, the devices have remained a niche among tech enthusiasts.
But even with a steep price tag, analyst firms such as International Data Corporation expect Apple will sell every foldable iPhone it can produce and secure a 40 per cent share of the lucrative niche by the end of next year.