Facebook and Instagram have been hit by a worldwide outage that has left potentially millions of people unable to access their accounts.

Users found they were mysteriously logged out and not able to log back in, or could not open the app at all.

The outage appears to be global, according to tracking website Down Detector.

The disruptions started around 10:00 am ET, with more than 300,000 reports of outages for Facebook and about 40,000 reports for Instagram, according to the website.

"We're aware people are having trouble accessing our services. We are working on this now," Meta spokesperson Andy Stone said in a post on X social media.