Instagram and Facebook messenger appear to have gone down, with thousands of users complaining about being unable to send or post messages.
The outage began shortly before 9.30pm, according to the tracking website Down Detector.
It appears to have affected people across the world, although most complaints were concentrated in the UK, US and Europe.
"I've been crying for 30 minutes annoyed with my Internet because I wasn't able to delete a story I posted unintentionally but in fact Instagram had fallen," wrote one devastated Instagram user on Twitter.
Another wrote: "You know Facebook messenger is down when the whole of Facebook runs to twitter so see if it's just them experiencing issues."
Neither Facebook nor Instagram responded to the complaints on Twitter or their websites.
However both services appeared to have been restored for users by around 10.30pm.
Outages were also reported by several major US phone carriers experienced outages a few hours earlier on Monday afternoon.
T Mobile, Verizon, AT&T, Sprint all suffered spikes in reported outages beginning around 12pm EST (5pm in UK).
Customers of the major carriers took to Twitter to complain that despite having full bars, they had no cell service.
In July last year Facebook, Instagram and Whatsapp all went down for almost a day.