An Apple spokesman told ABC News in an email the company "discovered a bug in development of watchOS 2 that is taking a bit longer to fix than we expected. We will not release watchOS 2 today but will shortly."
Apple's iOS 9 software update is unaffected by the bug and is set to be available later this morning, a company spokesman said.
Perhaps the biggest appeal of watchOS 2 is the ability for apps to run natively, meaning many can run entirely on the Apple Watch, allowing for a faster experience with even more functionalities.
Among the new capabilities available in watchOS 2 are photo faces, including time lapses of city scenes, the ability to see a different photo every time a user glances at their wrist and nightstand mode, turning a charging watch into an alarm clock.
A time travel feature will also let users turn their crown to leap forward and backward in time to see their schedules. Siri will also respond to a voice command to start counting a workout, without a user having to touch their Apple Watch.