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Justin Bieber is the world's top young musician under 21 according to a list compiled by the American magazine Billboard.

The Canadian singer was number one in the 21 Under 21 list for the second year running.

He beat previous X Factor UK acts like One Direction and Cher Lloyd to the top spot.

Billboard said the 18-year-old "remains more powerful in the pop universe than ever".

One Direction came second in the list, having become one of the biggest groups in the US over the past year.

Justin Bieber's 20-year-old girlfriend, Selena Gomez, came in sixth.

She was noted in the list for a busy year that has seen her release an album, create a fragrance and provide a voice for the animated film Hotel Transylvania.

Completing the top 5 are 20-year-old rapper Mac Miller, country artist Scotty McCreery, 18, and former Disney star Demi Lovato, 20.

1 - Justin Bieber

2 - One Direction

3 - Demi Lovato

4 - Scotty McCreery

5 - Mac Miller

6 - Selena Gomez

7 - Porter Robinson

8 - Cher Lloyd

9 - Earl Sweatshirt

10 - Nick Jonas

11 - Jackie Evancho

12 - Cody Simpson

13 - Mindless Behaviour

14 - Megan & Liz

15 - IU

16 - Bridget Mendler

17 - 3Ball MTY

18 - Miley Cyrus

19 - Madeon

20 - Ross Lynch

21 - Victoria Justice