Social media services Facebook, WhatsApp and Instagram have been hit by an outage lasting several hours.
All three services are owned by Facebook and could not be accessed over the web or smartphone apps.
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 across the world.
Some people also reported problems using Facebook's virtual reality headset platform, Oculus.
And apps which require Facebook logins were affected, including Pokémon Go.
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.