The new smartphones have Apple’s new pressure sensitive screen, called 3D Touch, as well as a redesigned camera.
Sam Shaikh, from Stratford, was the first to enter the Apple Store in Covent Garden, London, having been outside “since 8.30pm on Monday night”.
The 29-year-old was greeted by claps and cheers from the staff, as they welcomed the first of several hundred customers waiting outside.
Mr Shaikh said he was also the first person in the queue last year when the iPhone 6 launched.
The new iPhone is looking to repeat the success of the record-breaking launch of the iPhone 6 last year, which sold 10 million units in its first days of sale.
The firm has already said it believes it is “on pace” to match last year’s sales.
Several hundred people queued outside the Covent Garden outlet, with coffee being handed out to those who had waited overnight.
The launch marks the beginning of a busy autumn period for Apple, which also has a new Apple Watch coming in partnership with fashion brand Hermes, as well as a larger iPad Pro, which is due to launch in November.
Earlier this month, Chinese smartphone Huawei also announced a phone with a pressure sensitive screen - with experts suggesting it could spark greater competition in the smartphone market.