"This was not the result of a third party attack," Facebook said in a statement after its services were restored.
The outage "occurred after we introduced a change that affected our configuration systems," it added.
The breakdown, at around 0615 GMT reportedly lasted an hour and hit users in the United States, Europe and Asia, with both sites showing error messages.
With users disabled from posting selfies or the latest details of their personal lives, many rushed to Twitter to complain and joke, with "#facebookdown" and "#SocialMeltdown2015" rapidly trending.
Some joked about how they had been able to read real books during the enforced social media pause.
"Status Update: Facebook is Down!!!" Twitter user @kingpodge posted, in a photographed handwritten note.
"It's, like, really snowing in New York and now Facebook and Instagram are down. The hipster apocalypse has begun," tweeted another user, @jessbrammar, as a snowstorm swept across the east coast of the United States.
"Things to do during #SocialMeldown2015 1. Take a selfie 2. Melt down further because we can't instagram it," posted @YashiDP.
Lizard Squad squirm in
"#facebookdown and I hope it never gets up again! Imagine the lives that would be saved!" tweeted @nikonical.
Some suggested that hacking group Lizard Squad had been responsible for the outage, after a tweet on the group's Twitter account read: "Facebook, Instagram, Tinder, AIM, Hipchat #offline #LizardSquad."
Reports said that Tinder, AIM, Hipchat and My Space had also been affected.
Lizard Squad has claimed to be behind a series hacks of Microsoft and Sony gaming networks over Christmas.
The group also claimed an attack on the website of Malaysia Airlines on Monday, referencing the Islamic State jihadists and threatening to expose data taken from the carrier's servers.
But analysts downplayed the likelihood that Lizard Squad was responsible.
"It's in their interest to claim the Facebook breakdown even if it's not true because that gives them a communications boost," Gerome Billois, an expert in cybercrime at IT consulting firm Solucom, told AFP.
"But the main Internet players usually say if they've suffered an attack which affected their services."
Facebook "wouldn't take the risk of denying that kind of information", said Jerome Robert, from the Lexsi computer emergency response team.
"As for Lizard Squad, their tweet is not really a claim of responsibility. They certainly have notched up some victories but nothing at Facebook's level."
Facebook, which is headquartered in California, has more than 1.35 billion active users each month.
More than 80 percent of its daily active users are outside the United States and Canada.
Though much of its traffic is driven by seemingly banal or inconsequential posts, it is a vital tool for countless businesses and organisations and a key forum for communication in countries with repressive governments.
The last time Facebook was reported down was September 2014.