Meta says it has resolved a “technical issue” which caused Facebook, Messenger and Instagram to go down.
Hundreds of users worldwide were unable to access them for around two hours on Tuesday.
People trying to log onto the websites and apps were finding error messages and were unable to refresh their feeds as normal.
Meta also apologised to those who had been affected, saying it resolved the problem as quickly as it could.
Tracking website Downdetector indicated the outages had affected multiple countries.