NEW YORK (Reuters) - On a night when celebrities can let loose on their fashion choices, pop princesses and Hollywood actresses took it up a notch in the avant-garde department at New York's Met Gala on Monday (May 1).

The 2017 Metropolitan Museum of Art's Costume Institute ball was themed "Rei Kawakubo/Comme des Garçons: Art of the In-Between", a tribute to highly structured creations of the Japanese designer and her avant-garde label.

Pop singer Katy Perry, a co-chair of the ball, lived up to the theme's challenge with a custom Maison Margiela "Artisanal" ensemble by John Galliano.

Eric Wilson, fashion news director at InStyle, described this year's theme as "extremely challenging" compared to years past and agreed that Perry's outfit was courageously on point.

Rihanna was no slouch either, embodying Kawakubo's penchant for dramatic silhouettes in a custom Comme des Garçons floral dress with cutouts and oversized ruffles.

Reality TV star Kim Kardashian went against the theme, sporting a white dress by Vivienne Westwood with no clutch, no jewellery and no Kanye West, her fashion-loving husband.

Tennis star Serena Williams also served up drama with a baby bump under her green Atelier Versace dress.