SAN FRANCISCO (REUTERS) - Apple says 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.

A company spokeswoman said the bug was taking longer to fix than expected.

"We will not release watchOS 2 today but will shortly," the spokeswoman said.

The updated operating system is designed to help users customise their watch and allow apps to load faster.

Apple said last week that watchOS 2 would be available on Sept 16.

Apple limited the availability of the Apple Watch earlier this year after a component supplied by a Chinese company was found to be defective, the Wall Street Journal reported in April.

The company also had issues this year with a bug that could cause iPhones to crash when a message containing a specific string of text was received.

Last year, a bug in Apple's HealthKit health and fitness application platform prevented its release along with the iOS 8 operating system for iPhones and iPads.