Apple on Monday said it is working to fix a "bug" it said was among reasons some newly released iPhone 15 smartphones are heating up.

The iPhone maker will address the problem in an update to its iOS 17 mobile operating software and is collaborating with developers of some apps adding to the problem, according to the Silicon Valley tech giant.

"We have identified a few conditions which can cause the iPhone to run warmer than expected," Apple said in response to an AFP inquiry.

Some handsets of the freshly-launched iPhone may feel warmer for a few days after initial set-up due to increased background activity, according to Apple.

"We have also found a bug in iOS 17 that is impacting some users and will be addressed in a software update," Apple said.

"Another issue involves some recent updates to third-party apps that are causing them to overload the system."

Apps that seemed to be making chips inside iPhones heat up due to workloads included Instagram, Uber and an Asphalt 9 car racing game, according to online posts.

An Apple support page told users that it is common for iPhones to feel warm when initially being set up or when being used for graphics-intense apps like games.

"These conditions are normal and your device will return to a normal temperature when the process is complete or when you finish your activity," the support page explained.

Apple iPhone 15 models launched on September 22, their Lightning charger ports replaced by a universal charger after a tussle with the European Union.

The release comes as Apple faces declining sales of iPhones, with higher prices pushing customers to delay switching to newer models.

Along with rolling improvements to iPhone cameras and chips, Apple also said that the iPhone 15, which includes four varieties, have internal components that simplify repair and a new frame that allows the back glass to be easily replaced.