Weeks after Microsoft pushed out its Window Phone 8 operating system for mobile devices, some early adopters are reporting random rebooting issues.

Users of HTC 8X and the Nokia Lumia 920 handsets, the first to feature the new OS, are posting on Microsoft and Nokia support forums of issues with their smartphones.

One user posted on Nokia's site, "I have my Nokia Lumia 920 three days now and it already became unresponsible [sic] twice. I could not start the phone or anything. Only a hard reset (all three buttons at once) started the phone again. Should I turn back the phone for a replacement?"

"I've had my 8X for a couple of days, and it's been having multiple reboots," said a HTC 8X owner on Microsoft's support forum.

"Pretty sure it's a software problem as have seen people complaining of the Lumia 920 doing the same thing.

"Seems like Microsoft rushed WP8 a bit," the user added.

Users have struggled to pinpoint the reason their devices are doing this and neither Microsoft, Nokia or HTC has publicly commented on the issue.

A user calling himself "DuncanF62" on Microsoft's forum said the issue is definitely software not hardware related.

"I'm starting to log my 8X reboots. No pattern that I can see. Once or twice when using the phone (starting a call and starting an app) but more often when doing nothing. I.e. took it off charge this morning to see the 'Enter PIN' screen," said DuncanF62.

"Not too much of a hassle in as much as it hasn't crashed on me whilst I've been doing something important," he added.

Windows Phone 8 is Microsoft's completely revamped OS which it hopes will help it make ground against Google and Apple in the fiercely competitive smartphone market.

It's been developed closely alongside Windows 8, which was also recently launched for Desktop PC's, as a bridge between the new generation of touchscreen devices.

Google, which markets the Android OS, also recently released the new version - Jelly Bean. Like Windows Phone 8, users are already reporting bugs.

A post on Google's Google+ social network said that users cannot add contacts with a December birthday due to the flaw.