5 Seconds of Summer have spoken of their delight after headlining their first arena-sized show.

The lads played at the Ak-Chin Pavilion amphitheatre in Phoenix on Thursday (November 13) and it seems the momentous day struck something inside the Australians.

Drummer Ashton Irwin wrote on Twitter: "Can't explain how happy I am...Just a ratbag kid from Sydney playing in a band with his dudes in an amphitheater, I had a blast, thank you."

Michael Clifford meanwhile said: "Phoenix holy sh*t that might've been the best thing I've ever experienced."

Bassist Calum Hood added: "That was awesome. Currently getting naked in celebration."

The quartet meanwhile are due to embark on a full world headline arena tour in 2015.

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Watch 5SOS perform in Phoenix below: