Meta suffered an outage of all its social media platforms with users of Facebook, Instagram and Threads locked out of their accounts.
At about 12pm US east coast time (5pm Irish time), the sites seemed to be returning to normal, about two hours after the outage reports first emerged.
"Earlier today, a technical issue caused people to have difficulty accessing some of our services," Meta spokesman Andy Stone said in a post on X.
"We resolved the issue as quickly as possible for everyone who was impacted, and we apologize for any inconvenience," he added.
According to the DownDetector website, reports that Facebook was down peaked at around 500,000 at 3:30pm Irish time.
Instagram peaked at about 70,000 reports at the same time.
Threads, the rival to Twitter that was launched in 2023, also experienced reports of outages, though WhatsApp, Meta's messaging service, seemed spared.
Facebook experienced a similar outage in October 2021 which was attributed to technical issues, not a security hack as originally feared.
At the peak of the incident, Facebook's status page, intended for advertisers, said the site was suffering "major disruptions" and that "engineering teams are actively looking to resolve the issue as quickly as possible."
Users trying to access Facebook were asked to log in but were unable to sign in using the correct password.
On Instagram, mobile users were seeing their feeds not refreshed.
Reports said that Meta's virtual reality headsets were also suffering problems, with the device's Horizon World platform not allowing users to sign in.
Facebook is the world's largest social media platform, with 3 billion active monthly users.
Instagram has about 1.35 billion users, according to the latest data.
X, formerly Twitter, saw a spike in online activity as users were locked out of the Meta sites.
"Testing, testing... affirmative, everything is functioning smoothly here," wrote X CEO Linda Yaccarino, taking a dig at its rival.
US media focused on the fact that the outage took place on Super Tuesday, the day that millions of people were voting in primaries in 15 states and one territory.
