Instagram briefly stopped working, leaving people unable to see people's pictures or profiles.
Users were instead greeted with empty profiles and a message that the app "cannot refresh feed".
The web version of the app also had problems. Heading to any page brought up only a "5xx Server Error".
Issues were particularly affecting users in northern Europe, Australia and the west coast of the US, according to the outage-tracking website Down Detector. But that is probably because of time zones – in California, where Instagram is based, it was past midnight when the problems started.
The problems come amid a difficult time for Instagram. The company's two founders left in recent days amid rumours that it disagreed with Facebook over how the company should be run.
And after the Facebook hack was revealed over the weekend, it emerged that Instagram users and accounts might also have been caught up in it if they had used their Facebook log-in to create their Instagram account.
It's not thought that those issues have anything to do with the current outage, which is almost certainly simply a technical fault. Instagram goes down for time-to-time and can send major ripples across the internet, since more than a billion people use it each month.
