According to server status checking site, Isitdownrightnow.com, Instagram was down for everyone around the world for over 3 hours.
Later, confirming the down status of the website, Instagram tweeted,
We’re working to fix a feed delivery issue. Thank you for your patience.
— Instagram (@instagram) April 12, 2014
Now, after 3 hours of service disruption, the service is back online, completely, for everyone.