Retail giant Hennes & Mauritz has sued its fast-growing rival Shein in a Hong Kong court for copyright infringement, the Swedish fashion juggernaut said Tuesday.

Shein, founded in China in 2008, has swiftly claimed a top place in the global fast-fashion marketplace, offering low-priced collections attractive to young social media-savvy customers.

H&M confirmed on Tuesday it had opened a lawsuit against Shein and Zoetop Business, a Hong Kong-based company affiliated with the online retailer.

"We have an ongoing copyright infringement lawsuit towards Shein filed in Hong Kong," a H&M spokesperson said.

"We believe that Shein in multiple cases has infringed on our designs."

According to a Hong Kong court document, H&M had pointed to "the striking resemblance between the products showing they must have been copied" and the "sheer scale of (Shein's) unauthorised substantial reproduction of the copyright works".

A representative for Shein, which is now based in Singapore, said by email the company does not comment on pending litigation.

Copyright infringement lawsuits are common in the fast-fashion world but it is often smaller, independent designers lodging complaints against giant retailers, making H&M's suit against Shein unusual.

The Swedish high-street brand is among the world's most recognisable and has for years jousted with Spain's Inditex -- Zara's owner -- for the top spot.

But Shein's rapid rise from a brand favoured by TikTok influencers to a global household name for Gen-Z -- with a reported growth of $16 billion in 2021 -- has tipped the scales, placing it on H&M's heels.

Its cut-price merchandise and relentless expansion have also brought allegations from critics of forced labour and human rights abuses.

Three independent designers in the United States filed lawsuits against Shein this month, alleging that it has "grown rich by committing individual infringements... as part of a long and continuous pattern of racketeering".

Shein has also not commented on those accusations.