The carrier acknowledged that there was an “issue impacting wireless voice and data services for some customers.” Verizon didn’t specify what was causing the disruptions, but said in updates shared on social media that it had deployed its engineering teams and was working to resolve the problem “as quickly as possible.”

Outage tracker Downdetector showed that Verizon customers began to report issues with their service around noon E.T. Reports appeared to peak in the early afternoon and remained elevated later in the day — sitting close to 50,000 as of 4:30 p.m. ET.

Impacted users said their phones were in “SOS” mode or had other no signal messages. In New York, alerts warned that the outage may disrupt 911 calls — urging residents to try landlines and devices from other carriers, if available, or visit a local police or fire station in-person in case of an emergency.

Per Downdetector, other major hubs impacted by Verizon’s outage included Washington D.C., Chicago, Houston, Los Angeles and Atlanta. But consumers across the country said they were experiencing disruptions.

A handful of outage reports for other carriers also bubbled up on Wednesday — but companies like T-Mobile and AT&T quickly confirmed online that their services were operating normally. Both suggested that their customers may be encountering issues contacting people with Verizon’s service, however.

When cellular outages happen, some phone companies also urge consumers to try to connect to Wi-Fi and use internet calling. If Wi-Fi is still unavailable, there can be a limited number of other options — including sending messages via satellite on newer iPhones.