The launch of Apples iOS 8 for iPhones and iPads has been hit by a bug affecting the companys health and fitness tracking software HealthKit.

The bug has prevented the software being launched alongside the new operating system, with Apple saying the launch may well be delayed by up to two weeks.

HealthKit formed a central part of the promotion for iOS 8 when it was introduced at Apples WWDC, and has seen even more focus following the announcement of the Apple Watch, the companys first wearable device.

The software gathers data such as blood pressure and weight from various health apps on Apple devices, and can provide users with overall profiles on their health and fitness, or even deliver this information to healthcare professionals.

Apple has also pulled some healthcare apps from its App Store that have already built connectivity with HealthKit into their functionality, such as MyFitnessPal and Carrot Fit.

“The MyFitnessPal app, which supports integration with Apples HealthKit, was temporarily removed from the Apple Store this morning to address some minor issues,” said MyFitnessPal in a statement to Reuters. “We are working with Apple on a solution and will have an updated version of the app, without the HealthKit piece (for the time being), back on the app store shortly.”