Myer chief executive Richard Umbers has forged an unlikely alliance with global icon Katy Perry as the department store group spares no expense defending its turf from the international retailers and e-commerce giants snapping at its heels.

Myer's sponsorship deal with one of the world's biggest music stars is a sign of the extreme measures traditional retailers are taking to compete against newcomers like Amazon. Mr Umbers said Myer is the first department store in Australia, and possibly the world, to recruit a major pop star to boost flagging sales.