5 Seconds of Summer guitarist Michael Clifford says a new song written by the band is one of his favourites yet.

The group are currently working on the follow-up to their 2014 self-titled debut.

It seems the Australians' sessions are going well, with Clifford writing on Twitter on Wednesday (March 11):

"Big big happy birthday to @benjaminmadden @JoelMadden love these guys. Spending their birthday in a session writing a kickass song with us.

"I don't think I've ever been more stoked on a song then the one we've wrote today @benjaminmadden @Luke5SOS @JoelMadden @MisterMikeGreen."

5 Seconds of Summer meanwhile have also been writing with the likes of Simple Plan and Bonnie McKee.

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Watch 5SOS being interviewed below: