Facebook, its photo sharing application Instagram and messaging application WhatsApp went dark on Monday evening, for nearly six hours.
The giant social media platform went dark at around 8.50 pm IST.
Downdetector, the website monitoring group has said that this was the largest failure it had ever seen.
Facebook users began to regain partial reconnectivity to the other three apps.
The disruption was the second blow to the largest social media platform in as many days after a whistleblower on Sunday accused that the Facebook on repeatedly prioritizing profit over checking on hate speech and misinformation.
Mike Schroepfer, the Chief Technology Officer of Facebook tweeted, "To every small and large business, family, and individual who depends on us, I'm sorry."
He also added to the same tweet that it "may take some time to get to 100%."
The shares of Facebook that has nearly 2 billion daily active users, fell 4.9 percent on Monday.
It is biggest daily drop of Facebook since last November, amidst a broader selloff in technology stocks.
The security experts said the outage could be the result of an internal mistake, though wrecking by an insider would be theoretically possible.
The director of Harvard's Berkman Klein Center for Internet & Society, Jonathan Zittrain tweeted, "Facebook basically locked its keys in its car."
Facebook acknowledged its users soon after the outage started and said they were having trouble accessing its applications but did not provide any specific reasons about the nature of the problem or said about how many users were affected by the disruption.
Several Facebook employees who declined to be named said that they believed that the disruption was caused by an internal routing mistake to an internet domain that was increased by the failures of internal communication tools and other resources which were depended on that same internet domain in order to work.
As per to estimates from ad measurement firm Standard Media Index, Facebook, which is the second largest digital advertising platform in the world has lost around USD 545,000 in United States ad revenue per hour during the disruption.