Verizon Wireless customers across the United States were hit by a major outage on January 14, leaving tens of thousands of phones in “SOS” mode and users unable to make calls, send texts, or access mobile data.

More than five hours into the crisis, the cause of the outage and major disruption still had not been revealed to the public or to Verizon’s customers.

The disruption began shortly after 9 a.m. Eastern time and quickly spread nationwide, according to The New York Post.

The New York Times reported that outage-tracking site Downdetector recorded more than 170,000 reports at the peak as complaints poured in from coast to coast.

Users in major cities from coast to coast, including New York, Los Angeles, Chicago, Boston, and Washington, D.C., reported total signal loss, failed calls, and dead data connections.

Verizon acknowledged the outage in a brief statement, saying it was aware of an issue impacting service for some customers and that engineers were working to resolve it.

“We are aware of an issue impacting wireless voice and data services for some customers,” a Verizon spokesperson told The Post. “Our engineers are engaged and are working to identify and solve the issue quickly. We understand how important reliable connectivity is and apologize for the inconvenience.”