It was not immediately clear what was causing the outage, or how long until it would be fixed.
“We’re aware that some people are having trouble accessing our apps and products," Facebook communications exec Andy Stone said on Twitter.
"We’re working to get things back to normal as quickly as possible, and we apologize for any inconvenience.”
Editor's note: A previous version of this story incorrectly stated that Twitter was down. The story has been updated to reflect that Facebook, Instagram and WhatsApp were down.
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