Shein has confidentially filed papers with Britain's markets regulator in early June for a potential London listing, two sources said, as the online fast fashion retailer moves ahead with what could one of the largest IPOs globally this year.

The Chinese-founded company, which was valued at $66 billion in a fundraising round last year, had started engaging with its financial and legal advisors to explore a listing on the London Stock Exchange early this year, sources told Reuters in May.

It is not immediately clear when Shein, known for its $5 tops and $10 dresses, plans to launch the initial public offering (IPO).

Both the sources, who have knowledge of the deal, declined to be named as they were not authorised to speak to the media.

A spokesperson for Shein declined to comment. The Financial Conduct Authority (FCA), the UK markets watchdog, did not immediately respond to Reuters request for comment.

(Reporting by Kane Wu and Julie Zhu; additional reporting by James Davey and Huw Jones in London; Editing by Sumeet Chatterjee and Louise Heavens)