TikTok users in the US are migrating to a Chinese app called RedNote with the threat of a ban just days away.

The move by users who call themselves "TikTok refugees" has made RedNote the most downloaded app on Apple's US App Store on Monday.

RedNote is a TikTok competitor popular with young people in China, Taiwan and other Mandarin-speaking populations.

It has about 300 million monthly users and looks like a combination of TikTok and Instagram. It allows users, mostly young urban women, to exchange lifestyle tips from dating to fashion.

Supreme Court justices are due to rule on a law that set a 19 January deadline for TikTok to either sell its US operations or face a ban in the country.

TikTok has repeatedly said that it will not sell its US business and its lawyers have warned that a ban will violate free speech protections for the platform's 170 million users in the US.

Meanwhile, RedNote has welcomed its new users with open arms. There are 63,000 posts on the topic "TikTok refugee", where new users are taught how to navigate the app and how to use basic Chinese phrases.

"To our Chinese hosts, thanks for having us - sorry in advance for the chaos," a new US user wrote.

But like TikTok, there have also been reports of censorship on RedNote when it comes to criticism of the Chinese government.

In Taiwan, public officials are restricted from using RedNote due to alleged security risks of Chinese software.

As more US users joined RedNote, some Chinese users have also jokingly referred to themselves as "Chinese spies", a reference to US officials' concerns that TikTok could be used by China as a tool for spying and political manipulation.

RedNote's Chinese name, Xiaohongshu, translates to Little Red Book, but the app says it is not a reference to Chinese communist leader Mao Zedong's book of quotations with the same name.

But security concerns have not deterred users from flocking to RedNote.

Sarah Fotheringham, a 37-year-old school canteen worker in Utah, says the move to RedNote is a way to "snub" the government.

"I'm just a simple person living a simple life," Ms Fotheringham told the BBC in a RedNote message.

"I don't have anything that China doesn't, and if they want my data that bad they can have it."