Katy Perry's giant bottle steals the show at high-energy Isle of MTV

"Let's sweat together!" urged Katy Perry joyfully as she opened her headline Isle of MTV set in the middle of a record-breaking Maltese heatwave.

The US pop star joined thousands of fans packed into the Granaries on Wednesday for one of the biggest performances ever staged at the free concert.

From California Gurls to Firework, she delivered hit after hit to a cross-generational crowd over more than 90 minutes with an energy that defied any heat warning. 

Early in the set, Perry encouraged fans to keep drinking water from their bottles, joking that they should stay hydrated after already seeing two people faint in the crowd. The comment proved to be fitting foreshadowing for one of the show's standout moments.

Opening the concert as part of her Out of Office tour, Perry appeared in a star-spangled shirt and tie emblazoned with the words "I am not a robot". After California Gurls, she launched into a medley of Teenage Dream and Last Friday Night, setting the tone for a greatest-hits show.

She soon changed into an MTV-inspired outfit, previously worn in a campaign for the broadcaster.

Addressing her varied career, she told the audience: "Some of you may know me from I Kissed a Girl. Some of you may know me because I went into space. And some of you may know me because of my partner."

In a hint that former Canadian Prime Minister Justin Trudeau had indeed joined her for her Malta leg of the tour, she twice referred to him, saying how much she loved when he was at her concerts.

Fans had waited until around 9pm for Perry to take to the stage after warm-up performances from several Maltese artists, including Eurovision representative AIDAN.

AIDAN warmed up the crowd ahead of Katy Perry's headline performance. Photo: Anthony Harvey/Shutterstock for IOMTV Malta

The elaborate office-themed set featured oversized props including a laptop, telephone, window and giant water bottle.

The quirky production blended chart-topping hits with comic office skits, including a phone call with her daughter during work, an out-of-office email and a mini lecture on how to "make AI your tool".

The evening's most memorable moment came when Perry climbed inside the giant water bottle and crowd-surfed towards an enormous straw as part of a section that saw her perform Hot N Cold and I Kissed a Girl.

But the show was more than elaborate props and theatrical gimmicks. Perry worked the crowd throughout, waving a Maltese flag, inviting superfans on stage to dance with her and stepping into the audience to chat with concertgoers.

Katy Perry held aloft by some backup dancers in muscle suits. Photo: Anthony Harvey/Shutterstock for IOMTV Malta

One of those was 16-year-old Luke, who was left almost speechless after Perry jokingly declared he should be made mayor. 

The interaction also showcased Perry's vocal ability as she performed a stripped-back version of Roar among the audience. Another quieter moment came with an acoustic rendition of Thinking of You.

She quickly shifted back into high gear, spraying the audience with foam from a giant tube of sunscreen before bringing the concert to a fitting close with Firework and an accompanying fireworks display.