5SOS, 5th Harmony and Shawn Mendes high on Billboard's 21 Under 21

Billboard has shared its 21 Under 21 of 2015 list and the No.1 spot has been given to none other than Aussie pop-punk band 5 Seconds Of Summer.

The 'She's Kinda Hot' heartthrobs, who just landed the No.1 position on the UK charts with new album 'Sounds Good Feels Good', finished at No.2 last year, but have now taken the top spot and the magazine explained its reason for bumping them up: "Anyone who still thinks 5 Seconds of Summer is a passing fad hasn't been paying attention in 2015."

Fifth Harmony are at No.2, up three places from last year's No.5, and member Lauren Jauregui told the magazine that they're currently hard at work on their new studio album: "You'll have music to soothe your soul soon, everything will be fine, we love you to death and we're not going anywhere. I promise."

Canadian sensation Shawn Mendes finished at No.4 (he made an appearance at 8 in 2014) and Billboard confessed that "Mendes is still crushing it on social media (4.3 million Vine followers, 5 million-plus Instagram followers and 4.4 million Twitter followers), but even if the Internet went down tomorrow, this guitar-toting singer-songwriter would command an audience".

Hailee Steinfeld is at No.10, Becky G is at No.12, Austin Mahone is at 14, Echosmith came in at No.19, and Shamir is at No.21. You can check out the full list of 21 Under 21 here.

Watch 5SOS performing live below: