TikTok users in the US are migrating to a Chinese app called RedNote and are facing a ban in a few days.

The move by users calling themselves “TikTok refugees” made RedNote the most downloaded app in Apple’s US App Store on Monday.

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

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

Supreme Court justices will rule on a law giving TikTok a Jan. 19 deadline to either sell its U.S. operations or face a ban in the country.

TikTok has repeatedly said it will not sell its U.S. business, and its lawyers have warned that a ban would violate free speech protections for the platform’s 170 million U.S. users.

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

“To our Chinese hosts, thank you for the invitation – sorry in advance for the chaos,” wrote a new US user.

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

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

As more U.S. users joined RedNote, some Chinese users jokingly referred to themselves as “Chinese spies,” alluding to U.S. officials’ fears that TikTok could be used by China as a tool for espionage and political manipulation.

RedNote’s Chinese name, Xiaohongshu, means “Little Red Book,” but the app says it is not a reference to the book of the same name containing quotes from Chinese communist leader Mao Zedong.

However, security concerns haven’t stopped users from flocking to RedNote.

Sarah Fotheringham, a 37-year-old school cafeteria worker in Utah, says switching 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 have, and if they want my data so badly, they can have it.”

Marcus Robinson, a fashion designer from Virginia, said he created his RedNote account over the weekend to share his clothing brand and “stay ahead of the curve.”

Mr Robinson told the BBC he was only “slightly hesitant” to accept the app’s terms of use, which were written in Mandarin.

“I wasn’t able to really read them, so that worried me a little,” he said, “but I took my chance.”

While a ban won’t cause TikTok to disappear immediately, it will cause app stores to stop offering it – which could kill it over time.

But even if TikTok dodges a ban, it could prove helpless against users who switch to alternative platforms.

Some social media users tell the BBC they scroll RedNote more often than TikTok.

“Even if TikTok stays, I will continue to use my platform that I created on RedNote,” Tennessee engineer Sydney Crawley told the BBC.

Ms Crawley said she gained over 6,000 followers within 24 hours of creating her RedNote account.

“I will continue to try to build a following there and see what new contacts, friendships or opportunities it brings me.”

Ms Fotheringham, the cafeteria worker, said RedNote had “opened my world to China and its people”.

“I can see things now that I never would have seen,” she said. “Ordinary Chinese people, it was so much fun to find out about their culture, their life, their school and everything else.”

The community has been “super welcoming” so far, said Mr. Robinson, the designer.

“I’m loving RedNote so far… I just need to learn to speak Mandarin!”