Twitter was down for thousands of users globally on Thursday, according to outage tracking website Downdetector.com.
There were more than 50,000 incidents of people reporting issues with Twitter in the US, according to Downdetector, which tracks outages by collating status reports from a number of sources. Users in other countries, including the UK, Mexico, Brazil and Italy, also reported Twitter not working.
It was not immediately clear what caused the outage.
The outage comes days after Twitter sued Tesla Inc chief executive Elon Musk for violating his $44bn deal to buy the company and asked a Delaware court to order the world's richest person to complete the merger.
The outage began around 8am ET and prevented users from logging into the micro-blogging site on desktops and mobile phones. Users were getting an error message: "Tweets aren't loading right now."
Twitter did not immediately respond to a request for comment, but its status dashboard indicated that all systems were operational.
The company had suffered another widespread outage in February that it blamed on a software glitch.
Other big technology companies have also been hit by outages in the past year, with a near six-hour interruption keeping Meta Platforms' WhatsApp, Instagram and Messenger out of the reach billions of users in October.
Notorious for outages in its early years, Twitter used to use its popular "Fail Whale" illustration, a beluga being lifted by birds, for such incidents but discontinued the logo in 2013.
Those who could use Twitter jokingly blamed the outage on Musk. "Elon Musk creates Twitter outage," one user tweeted.
Twitter shares were marginally down at $36.60 before the bell on Thursday.