Social media services Facebook, WhatsApp and Instagram have been hit by an outage since 5pm GMT.
All the services are owned by Facebook and could not be accessed over the web or smartphones.
Downdetector, which tracks outages, logged nearly 80,000 reports for WhatsApp and more than 50,000 for Facebook.
Data from the website suggests the outage is affecting user accounts globally.
Users unable to post, or send messages but some could browse but that didn’t last long.
Facebook said: “We are aware some people are having trouble accessing our apps and products. We are working to get things back to normal as quickly as possible and apologise for any inconvenience.”
No official reason for the problem was given, but speculation is cyber war attacks on the giant.
But it’s likely to involve a configuration error with DNS, or technical glitch.