Many iPhone apps are crashing as soon as they are opened, apparently because of a problem at Facebook.
A wide variety of apps – which may use Facebook's platform for a host of different features – are broken because of a technical issue.
It appears to only be affecting iOS devices, as Android devices remain operational.
The problem has led many of the world's biggest apps, including Spotify, to crash as soon as they are launched.
"Something’s out of tune," Spotify's Status account said. "We’re currently investigating, and we’ll keep you posted here!"
Workarounds include going to Spotify's web player, or using Airplane Mode before opening the app.
However, users will only be able to play downloaded music, rather than content streamed from the internet.
The New York Times app, Hinge, Fitbit, Twitter, Strava, and Snapchat all appear to be affected.
Uninstalling and reinstalling the application does not fix the issue, companies have warned.
Facebook confirmed there was a problem on its status page, intended for developers.
"We are aware and investigating an increase in errors on the iOS SDK which is causing some apps to crash," a member of the Facebook team wrote.
Reportedly, the issue started approximately 11:20am.
Downdetector indicates that it is also having an affect on pre-loaded iOS apps, including the App Store and Apple Music. Safari, however, seems not to be suffering from the fault.
Video games, including Jurassic World Alive, Mario Kart Tour, Player Unknown's Battlegrounds (PUBG) and the Call of Duty mobile game are also reporting crashes.
Some users are reporting that using a blocker to stop apps from accessing Facebook's servers makes the apps operational again.
This is not the only time a Facebook SDK has resulted in crashes. A similar issue occurred in May when those same apps were inoperable.
"Earlier today, a new release of Facebook included a change that triggered crashes for some users in some apps using the Facebook iOS SDK. We identified the issue quickly and resolved it. We apologize for any inconvenience", Facebook wrote at the time.