Menlo Park, California - More than 10 million people have signed up to Threads, Meta's rival to Twitter, within the first few hours of its launch, the company's CEO Mark Zuckerberg said Thursday.

The much-hyped app went live on Apple and Android app stores in 100 countries on Wednesday evening, 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.

"10 million sign ups in seven hours," Zuckerberg wrote on his official Threads account 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 battle it out in a cage fight.

In his first tweet in over a decade, Zuckerberg posted a Spider-Man pointing at Spider-Man 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 had the opportunity to do this but hasn't nailed it. Hopefully we will."

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 widely understood to be 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."

"Twitter users are desperate for an alternative, and Musk has given Zuckerberg an opening," she added.

Under Musk, Twitter has seen content moderation reduced to a minimum with glitches and erratic decisions scaring away celebrities and major advertisers.

He has angered Twitter's most devoted aficionados by declaring that access to its TweetDeck app – which allows users to view a fast flow of tweets at once – would be for paying customers only.