Singer Justin Bieber performs at the 2012 Teen Choice Awards at the Gibson Amphitheatre in Universal City, California July 22, 2012.[Photo/Agencies]

Justin Bieber topped Billboard's "21 Under 21" list of the world's top young musical acts for the second year in a row, fending off stiff competition from British boy band One Direction.

Bieber, 18, "remains more powerful in the pop universe than ever", Billboard said, having released two No 1 albums in the last year - holiday set "Under the Mistletoe" and his latest pop album, "Believe".

"Bieber is the supernova of teen pop stars with charisma, popularity and swagger to spare ... it's Biebs' world, and we're lucky to live in it," the music publication said.

One Direction, whose five members range in age from 18 to 20, burst onto the U.S. pop scene just six months ago after first soaring to success in their native Britain. Managed by British TV entrepreneur Simon Cowell, One Direction made history in March when it became the first UK group to debut at the top of the Billboard 200 chart with its first album.

Singer Demi Lovato, 20, came in third on the list. The former Disney Channel star joined the judging panel on TV singing competition "X Factor" this year.

Rounding out the top five were country singer and "American Idol" winner Scotty McCreery, 18, and rapper Mac Miller, 20.

Below is Billboard's full "21 Under 21" list:

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 Behavior

14. Megan & Liz

15. IU

16. Bridgit Mendler

17. 3BallMTY

18. Miley Cyrus

19. Madeon

20. Ross Lynch

21. Victoria Justice