5 Seconds of Summer have debuted a new song as they opened their latest tour.

The lads performed 'Permanent Vacation' in Lisbon, Portugal on Monday (May 4).

The show was the first date of the Australians' Rock Out With Your Socks Out tour.

Bassist Calum Hood said on Twitter after the gig: "Perfect start to the tour! Fallen in love with you Portugal! Thanks for having us.

"Also hoping you like the new song, permanent vacation!"

Next up for 5 Seconds of Summer is a date in Madrid on Wednesday (May 6).

The band have been busy this year recording the follow-up to their 2014 self-titled album.

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Watch 5SOS perform their new song below: