Justin Bieber has a vocal coach with him constantly to help him through his voice breaking.

The 16-year-old 'Baby' Singer is currently struggling as puberty alters his vocal chords, but has a voice expert watching over him and ensure he can still perform his hits live.

A source told the News Of The World newspaper: "Justin is physically developing at a slower rate than most guys so his voice is only breaking now.

"He's working with the best in the business, a specialist called Jan Smith, to make sure he gets s much vocal rest as humanly possible for a working pop star.

"It's the same people who worked with Usher when his voice broke."

Despite his voice breaking, Justin is still appearing on stage, and will perform on British TV show 'The X Factor' tonight (28.11.10). He also stayed on to sign copies of his autobiography 'First Step 2 Forever' for an extra 1,000 fans at a New York bookstore on Friday (26.11.10).

During the marathon signing - which saw him autograph 2,000 copies of the book - Justin tweeted: "Sorry we are late. My fans are the most loyal passionate people ever. Super grateful. thank u. We got a lot more people to see. I'm not leaving until I keep my promise. Thanks for everyone being so cool about this. (sic)"

He later added: "Finished the signing in the New York. Had to show love. We let 1,000 more people in. Love y'all. wish I could let the whole world in."