The blog posted a screenshot showing an error message that appeared when users tried to install the latest version of the operating system for iPhone, iPad and the iPod touch.
Earlier Apple said it won't release watchOS 2, an updated operating system for the Apple Watch, on Wednesday as planned after it discovered a bug in development.

Apple Inc had unveiled the next update of the iOS iPhone and iPad operating system, which concentrates on optimising iOS to run smoother and faster with lower power consumption, adding an extra hour to the iPhone's battery life. An additional low-power mode will add another three hours of iPhone battery life.

The operating system will take up a 1.3GB of space to install on the device. iOS 8 required more than 4GB, which caused issues for users requiring them to delete apps.

The new search assistant that is an advance on Apple's Spotlight search facility, integrates with Siri to create a Google Now competitor, capable of displaying data from apps and the web, and controlled via text or voice. Siri can now offer directions based on invitations pulled automatically from email and leave reminders for the events.