More than 30 million people have downloaded Threads, Meta's rival to Twitter, within the first few hours of its launch, the company's CEO Mark Zuckerberg said on Thursday.

The app went live on Apple and Android app stores in 100 countries on Wednesday, and will run with no ads for now, but its release in Europe has been delayed over data privacy concerns.

Threads is the biggest challenger yet to Elon Musk-owned Twitter, which has seen a series of potential competitors emerge but not yet replace one of the world's biggest social media platforms, despite its struggles.

"Feels like the beginning of something special, but we've got a lot of work ahead to build the app," Zuckerberg wrote on his official Threads account on Thursday.

Accounts were already active for celebrities such as Jennifer Lopez, Shakira and Hugh Jackman, as well as media outlets including The Washington Post and The Economist.

Zuckerberg also offered a shot across the bow at Musk -- the pair are known to be bitter rivals, and have offered to wrestle it out in a cage fight.

In his first tweet in over a decade, Zuckerberg posted a Spiderman pointing at Spiderman meme in an apparent reference to the similarities between Threads and Twitter.

On Threads, he wrote: "It'll take some time, but I think there should be a public conversations app with 1 billion+ people on it."

Twitter has said it has more than 200 million daily users.

Threads was introduced as a clear spin-off of Instagram, which offers a built-in audience of more than two billion users, sparing the new platform the challenge of starting from scratch.

Instagram chief Adam Mosseri told users that Threads was intended to build "an open and friendly platform for conversations."

"The best thing you can do if you want that too is be kind," he said.

Zuckerberg is taking advantage of Musk's chaotic ownership of Twitter to push out the new product, which Meta hopes will become the go-to platform for celebrities, companies and politicians.

"It's as simple as that: if an Instagram user with a large number of followers such as Kardashian or a Bieber or a Messi begins posting on Threads regularly, a new platform could quickly thrive," strategic financial analyst Brian Wieser said on Substack.

Analyst Jasmine Engberg from Insider Intelligence said Threads only needs one out of four Instagram monthly users "to make it as big as Twitter." (AFP)