Chinese start-up Meitu is best known for an app that helps people "beautify" their selfies.

Whether it is to remove pimples, tweak their face shape or alter their skin tone, more than 450 million people use the app every month - mainly teenagers and young adults, predominantly female.

And despite struggling finding a way to make money from the app, Meitu has just listed on the Hong Kong stock exchange, raising $629m - which gives it a valuation of $4.6bn. That makes it the biggest IPO by a technology firm in the city in almost a decade.

Video journalist: Helier Cheung