Facebook and Instagram both started experiencing difficulty at around 4pm GMT on March 13.
Error messages on both sites stated: “Oops… Something went wrong. We’re working on getting it fixed as soon as we can.”
“Many users took to other social networks such as Twitter to vent their frustration at being unable to access the online services.
The hashtags #FacebookDown and #InstagramDown were used more than 150,000 times.
WhatsApp users also started reporting issues from around 6pm GMT, with some users claiming they were unable to send messages.
Responding to rumours posted on other social networks, Facebook said the outages were not a result of a cyber attack.
“We’re aware that some people are currently having trouble accessing the Facebook family of apps,” Facebook said in a statement sent to the Mirror Online at 7pm last night.
“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.”
A DDoS (Distributed Denial of Service) is a type of cyber attack that involves flooding a website with extremely high volumes of traffic.
“We are racing to spin up new machines as others go down. Mostly resolved… but it takes time,” the source said.
Network monitoring company ThousandEyes, which claims to act as the “X-Ray machine of the Internet”, said that the cause appeared to be internal rather than a network or Internet delivery issue.
“Given the sheer scale and continuous changes that these web scale providers are constantly making to their applications and infrastructure, sometimes things break as a result of these changes, even in the most capable hands,” a spokesperson for the company said.