"A networking issue" was to blame for the disruption of Facebook services, which the company began fixing within an hour, a spokeswoman said. The hashtag #facebookdown is a trending search term in the U.S.
However, as per Down Detector, an outage-tracking website, when a few users tried opening the application it showed "an error has occurred, please try again later".More news: Spotify kills Microsoft's Groove Music
Twitter user Ian Prince wrote: "Right now there are millions of people trying to awkwardly avoid looking at other people on their lunch break".
"Thanks for your patience as we improve the site". Instagram had 2,500 reports of problems.
"We're sorry for the inconvenience", a Facebook spokesperson said in a statement.
Facebook and Instagram went down on Wednesday, which meant people didn't know where to go to be outraged, post photos of their food, or get their news from Russian hackers.