Zuitao, a company that owns a karaoke app that is taking China by storm, has only about 15 people on its team, and they occupy just one modest room in a Beijing office tower. According to a rough calculation, that means each staffer is responsible for hundreds of thousands of users.

On May 31, Zuitao released a sophisticated karaoke app called Changba. Five days later, it was the number one free iPhone app in China. In the month and a half that has since elapsed, it has never left the top five, and on Monday, when I met with CEO Tony Chen, it was sitting pretty at number three.

Chen was nervous about sharing actual numbers for fear of attracting too much attention from potential copycats, but he said active users number in the millions. I heard from other sources that those millions could be creeping into double digits. Even in China, even in the mobile era, that is an astounding achievement.

Before starting Zuitao, Chen was a co-founder of a travel portal called Kuxun, which in 2009 was acquired by TripAdvisor. (I wrote about his Kuxun co-founder, Shichun Wu, in a story about the restaurant-recommendation app Shakey Shakey Food God.) The 34-year-old was previously an engineer with Alibaba and Microsoft Research Asia. He started Zuitao as a coupons search company and attracted $2 million of funding from BlueRun Ventures, but the site’s growth rate ultimately proved too slow for China’s hyper-competitive market.

Changba was a hell of a pivot. In the app, users can select from a range of 2,000 songs, all of which Zuitao has paid to license. They can then sing the song into the phone, save it, add a photo slideshow, and share it with friends and Changba’s fast-growing community. Some of the most popular song versions feature on the homescreen, which also provides links to recently uploaded songs and new users.

Fellow karaoke citizens can leave comments on the song and show their appreciation by rewarding the singer with virtual flowers. They’re free for the time-being, but each user is limited to three flowers a day. This system of virtual rewards will ultimately be key to Changba’s revenue model.

Perhaps Changba’s most compelling feature is its filtering technology, which can make even the crappest singers sound half decent. I presume it is similar to what Britney has been using in the studio for decades. Chen likens it to “Instagram for sound”.

Clearly, in karaoke-crazy China, this is a winning product. Despite Chen’s protectiveness over figures, copycats are sure to follow. In the Western world, its closest analogues are Karaoke Anywhere and Glee Karaoke.

Chen boldly claims that company could be worth $1 billion within four-to-five years. Certainly, investors are paying attention. According to a report from ChinaVenture, Sequoia put $15 million into the startup’s Series B funding round.

Because of music copyright restrictions, the app is not available outside of China. In the meantime, then, you’ll have to satisfy yourself with the below demo video, which I shot on-the-fly during lunch with Chen. Not quite as good as the real thing, but close. Very close. Ish.