Threads, the Twitter rival, had five million signups in the first four hours after it launched, according to Mark Zuckerberg, CEO of Meta.
Meta is looking to lure users away from Elon Musk's troubled platform by offering an app that bears close resemblance to the competitor.
Threads is available in 100 different countries on the Apple and Google Stores, although current EU policies mean that the app will not be available in EU countries.
Brands like Billboard, HBO, NPR and Netflix had accounts created within minutes of the app's launch. Meta said the first celebrity endorsers included Shakira and Gordon Ramsay, while a recent report said Oprah Winfrey and the Dalai Lama had also signed up.
Threads comes days after Twitter faced heavy criticism from users. Last week, Twitter began requiring users to log in to view posts — previously, people without Twitter profiles could view posts. It then imposed restrictions on non-paying users of the platform. Since Elon Musk took over Twitter, thousands of users have closed their accounts on the app.
People will be able to use their Instagram to log into Threads and follow existing contacts.
Posts on Threads can be 500 characters long, compared to 280 for most Twitter users, and videos of up to five minutes can be posted.
