Microsoft's Windows Phone 9 will be released in preview form early next year, according to a report, Digital Spy said.

Unnamed sources speaking to NokiaPowerUser have claimed that the initial build of the mobile operating system will debut in January 2015.

The report states that all existing Windows Phone 8 devices will be upgraded to Windows Phone 9, but notes that some features may be absent on certain phones.

For instance, the rumoured split-screen multitasking feature is said to be unavailable on devices with a smaller display.

Microsoft's next edition of Windows Phone is expected to have closer ties with the desktop version of Windows, with some sources claiming that the two platforms could even be merged.

The computing giant is holding a Windows-themed press conference on September 30, where the future of the operating system will be mapped out.