Facebook, Instagram and WhatsApp are all back online and working as normal after a 14-hour outage left many users unable to post updates.
Facebook and Instagram both started experiencing difficulty at around 4pm GMT, according to data from website Downdetector, which monitors online outages.
Error messages on both sites stated: “Oops… Something went wrong. We’re working on getting it fixed as soon as we can.”
WhatsApp users also started reporting issues from around 6pm GMT, with some users claiming they were unable to send messages.
“We’re aware that some people are currently having trouble accessing the Facebook family of apps,” Facebook said in a statement.
“We’re focused on working to resolve the issue as soon as possible, but can confirm the issue is not related to a DDoS attack.”
It has been described as Facebook’s “most severe outage in history”.
The last time Facebook had a disruption of this magnitude was in 2008, when the site had 150m users – compared with around 2.3bn monthly users today.
Responding to rumours posted on other social networks, Facebook said the outages were not a result of a cyber attack.
“We’re focused on working to resolve the issue as soon as possible, but can confirm that the issue is not related to a DDoS attack,” it said in a statement on its Twitter account.
However, it is not yet clear what caused the issues for users of the social network around the world.
A source told NBC Bay Area last night that Facebook’s its database was “overloaded”.
“We are racing to spin up new machines as others go down. Mostly resolved… but it takes time,” the source said.
Facebook, which gets much its revenue from advertising, was still investigating the overall impact today “including the possibility of refunds for advertisers”.