Some companies have reportedly been given special access to the Apple Watch labs to fine-tune their apps, Digital Spy reports.

According to Bloomberg, Facebook, BMW and United Airlines are among the firms which have been invited to Apple's headquarters in Cupertino, California.

Security is apparently tight - internet access is completely blocked inside the labs and it is forbidden to bring external material inside.

Developers are only allowed to bring their app's source code with them on a hard drive but they are not allowed to take it off the premises after.

Instead, Apple is keeping hold of the code themselves and will send it on to the individual companies nearer to the Apple Watch's release date.

Apple is set to reveal more details about its first wearable - including a possible release date - on Monday, March 9.