The shutdown of Elon Musk's platform started early on Saturday, making it largely inaccessible on both the web and through mobile apps after the billionaire refused to name a legal representative to the country, missing a deadline imposed by Supreme Court Justice Alexandre de Moraes.
The blockade marks an escalation in a months-long feud between Musk and de Moraes over free speech, far-right accounts and misinformation.
Brazil is one of the biggest markets for X, with tens of millions of users.
"I've got the feeling that I have no idea what's happening in the world right now. Bizarre," entertainment writer and heavy X user Chico Barney wrote on Threads.
Threads is a text-based app developed by Instagram that Barney was using as an alternative.
"This Threads algorithm is like an all-you-can-eat restaurant where the waiter keeps serving things I would never order."
Bluesky, a social media platform that was launched last year as an alternative to X and other more established sites, has seen a large influx of Brazilians in the past couple of days.
The company said on Friday it has seen about 200,000 new users from Brazil sign up during that time, and the number "continues to grow by the minute." Brazilian users are also setting records for activities such as follows and likes, Bluesky said.
Previous users of other platforms welcomed Brazilians to their ranks. "Hello literally everyone in Brazil," a user wrote on Threads.
"We're a lot nicer than Twitter here," said another.
Platform migration isn't new for Brazilians. They were huge adopters of Orkut and, when Orkut went kaput, they very gladly moved to other platforms.
X is not as popular in Brazil as Facebook, Instagram, YouTube or TikTok.
However, it remains an important platform on which Brazilians engage in political debates and is highly influential among politicians, journalists and other opinion makers.
Pop stars and their fanbases were also hit by Brazilians being left off the platform.
"Wait a lot of my fan pages are Brazilian!!! Come back hold up!!," Cardi B said Friday on X.
A fan page dedicated to Timothée Chalamet, known by the handle TimotheeUpdates, said it would temporarily cease updating as all of its administrators are Brazilian.
De Moraes said X will stay suspended until it complies with his orders, and he also set a daily fine of 50,000 reais ($A13,158) for people or companies using virtual private networks, or VPNs, to access it.
Some legal experts questioned the grounds for that decision and how it would be enforced. Others suggested the move was authoritarian.
The Brazilian Bar Association said in a statement that it would request the Supreme Court review the fines imposed on all citizens using VPNs or other means to access X without due process.
Brazil's bar association argued that sanctions should never be imposed summarily before ensuring an adversarial process and the right to full defence.
With AAP.