A new app billed as a rival to Twitter has seen more than five million people sign up in its first few hours.
Threads, created by Facebook and Instagram owners Meta, went live in the UK at midnight on Thursday.
Linked to Instagram, it allows users to post up to 500 characters of text and up to five minutes of video and links, as well as pictures.
Chef Gordon Ramsay, pop star Shakira and Mark Hoyle, better known as the YouTuber LadBaby, have already joined and made their presence on the app known.
Posting on the app, Facebook boss Mark Zuckerberg said: “Just passed 5 million sign ups in the first four hours.”
He said earlier: “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.”
The new app is the latest chapter in the rivalry between Mr Zuckerberg and Elon Musk, who bought Twitter in October.
Last month, the pair – two of the world’s most high-profile billionaires – agreed to take each other on in a cage fight in an exchange that went viral on social media.
Users of the new app will be able to use their Instagram login to get started and, like on the picture-sharing platform, can follow and connect with friends and influencers with similar interests.
In the UK, all users under 18 will be defaulted onto a private profile when they join.
Someone’s feed on the app includes threads from people they follow as well as recommended content from creators they have not yet heard of.
Threads posts can be shared on a user’s Instagram story and as a link on other platforms.
People can control who mentions them and who can reply to them on the new app, replies to threads containing specific words can be filtered out and other users can be unfollowed, blocked, restricted and reported.
Any accounts a user has blocked on Instagram will automatically be blocked on the new app and Instagram’s safety guidelines will be enforced on the new platform, Meta said.
Eventually, the California-based company wants it to be possible for people without a Threads account to interact on the platform, which it hopes will usher in a “new era of diverse and interconnected networks”.
If and when this happens, if a user has a public profile their posts will be accessible from other apps while if they have a private one they will have to approve new followers.
Earlier this week, social media consultant and industry analyst Matt Navarra told the PA news agency the app is the “first credible threat” to Twitter.
He said: “I think that Threads is the first real, credible threat to Elon Musk’s Twitter.
“Users of Twitter are desperately looking for an exit from the platform to escape, and the existing options of rivals are fairly limited.
“They all have the same big problem, which is you have to start from zero – it’s a network that is completely new.
“One of the biggest benefits for Meta is that it’s building off the back of Instagram, where people are familiar and can also kick-start their following because it ties into the same social graph.”
He said that while users have an appetite for change, it would be weighed up against mixed public opinions on Meta.
He added: “Meta and Instagram comes with baggage, a bad name and bad press. People are very wary and sceptical of anything [Meta owner] Mark Zuckerberg does.”
The arrival of the new app comes after Twitter announced TweetDeck is to become the next part of the company to be limited to users who have paid for verified status.
Two days earlier, Mr Musk announced users would be limited to reading just 600 posts a day.
Press Association – Gwyn Wright and Cormac Pearson