Major social media services including Facebook, Instagram and WhatsApp were hit by a massive outage on Monday, tracking sites showed, impacting potentially tens of millions of users.
Outage tracker Downdetector was showing outages in heavily populated areas like Washington and Paris, with problems being reported from around 15:45 GMT.
Users trying to access Facebook in affected areas were greeted with the message: "Something went wrong. We're working on it and we'll get it fixed as soon as we can."
The outage comes a day after a whistleblower went on US television to reveal her identity after she leaked a trove of documents to authorities alleging the social media giant knew its products were fuelling hate and harming children's mental health.
Frances Haugen, a 37-year-old data scientist from Iowa, has worked for companies including Google and Pinterest - but said in an interview with CBS news show "60 Minutes" that Facebook was "substantially worse" than anything she had seen before.
The world's largest social media platform has been embroiled in a firestorm brought about by Haugen, with US lawmakers and The Wall Street Journal detailing how Facebook knew its products, including Instagram, were harming young girls, especially around body image.
"We're aware that some people are having trouble accessing our apps and products," Facebook spokesman Andy Stone said on Twitter.
South African users have also been affected.
We’re aware that some people are experiencing issues with WhatsApp at the moment. We’re working to get things back to normal and will send an update here as soon as possible.— WhatsApp (@WhatsApp) October 4, 2021
Thanks for your patience!
We’re aware that some people are having trouble accessing Facebook app. We’re working to get things back to normal as quickly as possible, and we apologize for any inconvenience.— Facebook App (@facebookapp) October 4, 2021
This article was updated at 22:56.