You might have noticed that many young Chinese people replaced their profile photos overnight with a 3D portrait of themselves and have begun sharing virtual selfies with their friends. But without any obvious watermarks or branding, this whirlwind trend has left people puzzled about what app everybody is using.

The answer is Zepeto, a S. Korean app that uses facial recognition to create virtual avatars. The app has been number one on the free downloaded apps chart on the Chinese Apple Store over the past few days, and become the hottest trend among Chinese millennials along the way.

The app, designed by S. Korea's Snow Corporation, was a sensation in the U.S. and Asia before it landed in the Chinese market, and in it you can also take selfies and groufies with your friends, strangers and even some celebrities, such as members of K-pop group BTS and American singer Ariana Grande.

Users can simply log in the app via their WeChat, Facebook and Twitter accounts and easily create avatars of themselves thanks to the facial recognition software, and then edit almost everything, including facial contours, hairstyles, makeup, clothes and even the decorations in the background of the photo.

However, it isn't simply an image editing tool. Users need gold coins – the only virtual currency in the game – to buy those hairstyles, outfits and furniture, and the fancier the item, the more expensive it is. The app gives a certain amount of gold coins to each user daily, but if you want to buy those products without saving for days, you can also buy the virtual currency with real money. A standard of the mobile game format.

Like other apps that are popular with China's youth, Zepeto features social networking options, such as chatrooms for friends or meeting new people, an emoji creator and the ability to like other people's snaps in a manner similar to Instagram and Facebook.

These options have reminded people of Qzone, a Tencent-backed Chinese social networking platform, which shares some similar features with Zepeto, but is no longer popular, partly because it only creates 2D images.

In fact, Zepeto's immense popularity has caused servers to overload, significantly slowing the creation and sharing process. In a bid to curb the issue, the Snow Corporation said they plan to release a an exclusive Chinese version of the app before the end of the year. But, considering how fast trends come and go in China, even that may be too little too late.