Some users were told the website was undergoing "required maintenance" on Saturday afternoon as they attempted to log on.
Down Detector, a website that tracks internet outages, reported a large spike in users being unable to access Facebook at about 2pm.
Most users reported a "total blackout", meaning the site would not load, or that they were unable to log in to their accounts.
The technical problems appeared to be affecting Facebook's desktop site and mobile application.
Some users of Instagram, the picture-sharing app owned by Facebook, have also reported problems.