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TikTok, known for its quirky 15-second videos, has been illegally and secretly harvesting vast amounts of personally identifiable user data and sending it to China, according to a proposed class-action lawsuit filed in California federal court last week.

The lawsuit also accuses the company and its Chinese parent company ByteDance of taking user content such as draft videos without their consent and having "ambiguous" privacy policies. It raises concerns that data gathered by TikTok could be used to identify, profile and track users in the US. The company is benefiting from this alleged activity because it uses this data to sell targeted ads, the lawsuit alleges.

"TikTok's lighthearted fun comes at a heavy cost," according to the lawsuit, which was filed on Friday.

The allegations against the popular short video app are the latest example of the growing security concerns surrounding TikTok, which surpassed 1.5 billion downloads worldwide in November. The US government is also reportedly looking into the app for potential security risks.

Misty Hong, a college student and resident of Palo Alto, California, is suing ByteDance, TikTok and Musical.ly, a lip-sync app that was rebranded as TikTok, for allegedly violating a federal computer fraud law, the California Constitution's right to privacy and other laws.

TikTok videos often include close-ups of people's faces, allowing the company to gather biometric data on its users, according to the lawsuit. Once a user shoots a video and clicks the "next" button, the videos are transferred to various domains without their knowledge. This happens before users even save or post a video on the app, the lawsuit states.

Hong downloaded TikTok in March or April 2019 but never created an account, according to the lawsuit. Months later, she discovered TikTok made one for her. She created five or six videos using the app but never saved or published the videos. Still, TikTok secretly took the videos and her data without her knowledge and sent the information to servers in China, according to the lawsuit.

TikTok is gathering a trove of data about its users, including their phone and social network contacts, email addresses, IP address, location and other information, according to the lawsuit. The company allegedly uses different tactics to conceal that they're transferring user data. Even when a user closes the app, it still harvests biometric and user data, the lawsuit states.

Citing articles from news outlets such as CNBC, Quartz and Affinity Magazine, the lawsuit alleges user data was sent to China. It lists several Chinese servers the data was transferred to before and after February 2019.

TikTok and Hong's lawyers didn't immediately respond to a request for comment.