Facebook, Instagram and WhatsApp have gone down around the world, with thousands of users reporting technical problems.
UK users were among those unable to access the social media platforms on Sunday.
The monitoring website Down Detector also reported issues across Europe, the US, the Middle East, Southeast Asia, and Brazil.
More than 6,000 Facebook users worldwide logged problems, with many reporting a "total blackout" and others unable to log in. The reports began to spike at about 11am.
More than 4,000 Instagram outages and 6,000 WhatsApp issues - mostly connection problems - have also been reported to Down Detector. The apps are both owned by Facebook.
Many users complained about the issues on Twitter, where #FacebookDown and #InstagramDown were among the trending topics.
A Facebook spokesman said: "Earlier today, some people may have experienced trouble connecting to the family of apps. The issue has since been resolved. We're sorry for any inconvenience.”
