TikTok, the viral short video app run by Chinese upstart ByteDance Inc., saw global user-downloads fall for the first time since its inception two years ago, new data from Sensor Tower shows.

The app amassed an estimated 177 million first-time users across the Apple App Store and Google Play for the third quarter ended September. That represents a 4% decline from a year ago. It’s the first time the hit app saw new installs drop on a quarterly basis, the mobile data provider said. In total, TikTok has been installed by around 564 million users so far this year and has been installed 1.45 billion times since launching.

TikTok has been the source of some controversy. It was briefly banned in India for spreading explicit content and US politicians have recently criticized the app for censorship. (Picture: Joel Saget/AFP)

TikTok has evolved to become a global phenomenon known for lighthearted content -- including lip syncing and dancing -- uploaded by teenage users from Boston to Bangalore. It’s also one of the few examples of a Chinese social media platform that has achieved global success. Beijing-based ByteDance is the world’s largest startups with a valuation of $75 billion according to CB Insights.

ByteDance is spending hundreds of millions of dollars to advertise TikTok on Facebook and Instagram, essentially buying users away from its biggest rivals. But the company may have to rethink that strategy after Facebook Chief Executive Mark Zuckerberg called out the Chinese app over privacy and freedom of speech concerns.

Zuckerberg’s remarks came after TikTok drew criticism for its alleged censorship of politically sensitive content such as videos of pro-democracy protests in Hong Kong to appease Beijing. TikTok has denied those allegations. It announced last week it has formed a team that includes two former U.S. lawmakers to review its content moderation policy.

A ByteDance spokeswoman said TikTok doesn’t comment on third-party numbers.

“With any app growth, there will come a time when it plateaus, especially since TikTok had grown so much,” said Alvin Foo, managing director of Reprise Digital, a Shanghai-based online marketing agency under the Interpublic Group of Cos Inc. “They should worry more about monetization and evolving.”