From 4pm BST this afternoon (August 1), users trying to access the site were met with an error message.
The generic "Sorry, something went wrong" holding page was previously seen during the social network's last period of unscheduled downtime on June 19.
The hashtag #facebookdown once again began trending on rival site Twitter, as people across the globe searched for updates on the situation.
"We're working to get things back to normal as quickly as possible," said a spokesperson for the company, before the live site returned at approximately 5.40pm BST.
June's outage was the longest the site had suffered for four years, with users left waiting for 31 minutes before access was restored.
Today's failure looks set to eclipse that record, although some users reported having no problems accessing the site as late as 5.15pm BST.