AT&T’s cellular network began experiencing major service problems for customers across the United States early on Thursday morning. Wireless customers took to the carrier’s forums, Reddit (1) (2) (3), and elsewhere to report that they’d lost all voice and mobile data service — with some of those impacted unable to reach 911 emergency services.

“We are aware of an outage currently impacting our mobility users and are working to resolve it ASAP,” the company wrote in a banner notification on its support forum. But its other support channels on social media were surprisingly quiet about the outage, which had already lasted several hours for many as of the time this story was published.

Such far-reaching disruptions are relatively rare among the major US carriers — T-Mobile experienced something similar last year — but they can prove extremely frustrating when they do occur. Outages that prevent consumers from reaching 911 also tend to draw the scrutiny of the FCC. In some regions, local emergency services have already emailed nearby residents warning of the AT&T situation and advising them how they can otherwise reach help if needed.

The Verge has reached out to AT&T for more details.