At a time when Twitter is already faltering, Mark Zuckerberg dealt Elon Musk another blow as he launched Threads, a long-awaited Instagram service that challenges Twitter, a move that would further intensify the competition between the two tech billionaires.

Zuckerberg wrote Wednesday in his first post on the new app, "Let's do it. Welcome to Threads." He attached the phrase to a fire emoji and said the app recorded 5 million subscriptions in the first 4 hours.

The app is very similar to Twitter, in that it allows short text posts that users can like, repost, and reply to, but it doesn't include any capabilities to send direct messages.

The post can be up to 500 characters long and include links, images and videos of up to 5 minutes long, according to a Meta publication.

The post said the app is available in more than 100 countries on both Apple's App Store and Google Play Store.

While Threads was launched as a standalone app, users can log into it with their Instagram credentials and follow the same accounts, making it an easy addition to more than two billion monthly active users to Instagram.

The head of financial analysis at the investment firm said, "A. J. Bell Danny Hewson, "Investors can't help but be a little excited about the possibility that Meta really has a 'Twitter killer'."

The release of Threads comes after Zuckerberg and Musk exchanged harsh criticism for months and even threatened to fight a real-life fight in a mixed martial arts cage in Las Vegas.

Twitter Challenges

Musk bought Twitter for $44 billion in October, but the platform's value has since plummeted, facing a mass exodus of advertisers amid deep staff cuts and disagreements over moderation in content.

In his subsequent posts on Threads, Zuckerberg addressed these challenges, writing, "I think there should be a public conversation app with more than a billion people. Twitter had a chance to do so but it didn't work. I hope we succeed."

Brands such as Billboard, HBO and Netflix got accounts within minutes of launching the app, as did celebrities like Shakira.

Based on a Reuters inspection of the app, it appears to show no ads.