Apple says it will replace iPhone Duo handsets that have developed problems with their screens just days after the highly-anticipated smartphone went on sale.

Photos posted by social media users 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 is aware of “an issue impacting the inner display on a small number” of units and urged affected users to contact the company for a replacement.

The Duo’s launch, which attracted long queues at Apple stores around the world last week, comes as the brand tries to reinvigorate its catalogue and challenge the foldable phones offered 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.

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 flaws in the 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.