Facebook has said it has fixed a problem which prevented users around the world updating their status or interacting with friends.
Some of the website's estimated 1.15 billion members were shown an an error message which read: "Couldn't update status. There was a problem updating your status. Please try again in a few minutes."
Some users also said they were unable to 'Like' posts, post comments or upload photos, although others experienced no difficulties using the website.
Hundreds of comments about the apparent service outage appeared on Twitter every few minutes during the outage.
A spokesman for Facebook said: "While performing some network maintenance, we experienced an issue that prevented some users from posting to Facebook for a brief period of time.
"We resolved the issue quickly and we are now back to 100%.
"We're sorry for any inconvenience we may have caused."
Michael Allen, a director at Compuware Corporation, which tracks internet down time using its Outage Analyzer tool, said the technical problems would have had an "enormous impact" on millions of people.
He said at least 3,500 other websites were affected, "although the actual number is likely to be far greater".
"This is because many other businesses and websites are connected to Facebook through the integration of its services," he said.
"For example, Facebook is used to enable people to login to many other sites and applications."
Founded in 2004 by Mark Zuckerburg, Facebook has around 700 million daily active users, according to its own figures.
It stores more than 100 petabytes (107 billion megabytes) of photos and videos at its three US data centres in Oregon, North Carolina and Iowa, as well as a fourth in Lulea, Sweden.
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