Apple has acknowledged some of its iPhone Duo handsets have developed problems with their screens, just days after the highly-anticipated smartphone went on sale.

Photos posted on social media show lines that appeared on the screens of the technology giant’s first ever foldable device, which has a starting price of £1,999 ($2,668) in the UK.

Apple said it was aware of “an issue impacting the inner display on a small number” of the phones and urged affected users to contact the company for a replacement.

The Duo’s launch, which attracted crowds at Apple stores around the world last week, is an attempt to reinvigorate the brand’s device range and challenge the foldable phones made by rivals.

Some Duo owners also posted photos online showing cracks along the screen’s centre crease, while others reported a crunching noise when opening the device.

An iPhone Duo user, Justin Lokos, posted an image of a device with lines across the right side of the display and later uploaded a picture of a new handset alongside the broken one, thanking an Apple store in New York for its help.

The extent of the issue remains unclear. Apple did not say how many devices were affected, while some images showing faulty devices may have been created using AI.

Francisco Jeronimo, technology analyst at market research firm IDC, said that meant some caution was needed before drawing conclusions about the whole production run.

But he added the early reports of issues also showed “that even a company with Apple’s engineering resources and supply chain discipline faces a steep learning curve in foldables”.

The Duo’s 7.6-inch (19.3cm) inner display is held together by a central hinge – a complex piece of engineering that has resulted in similar flaws in folding devices made by some of Apple’s competitors.

Samsung’s first foldable phone, the Galaxy Fold, suffered an early setback in 2019 when reviewers reported broken screens on the devices.

Android users already have a broad selection of foldable phones to choose from, technology that Apple spent years developing before the Duo’s release.

It is Apple’s most expensive iPhone ever, costing up to £3,199 for the most well-equipped models.

Jeronimo said because Apple had positioned the Duo as a “premium alternative” to established foldables, “how it handles this first-generation issue will shape buyer confidence in the category well beyond its own sales”.

“Apple has a loyal customer base and a retail network that can swap devices on the spot, but with a further 28 markets launching on 30 October, it needs to clarify its warranty position quickly,” he said.

The Duo marks Apple’s first major iPhone redesign in almost two decades and was unveiled by new chief executive John Ternus, who took over from Tim Cook in September.

When closed, the Duo looks like a wider version of an iPhone, then opens up to a device resembling a small tablet computer.

“Others have created foldables that just feel like two phones awkwardly stuck together”, Ternus told an audience at Apple’s California headquarters last month.

The Duo, he said, would “redefine the experience of using a foldable phone”.