The number of cases peaked at more than 100,000 Monday morning, according to the website Downdetector. Users complained of being unable to make calls or send texts.
Thousands of Verizon users across the United States reported having little or no cellphone service on Monday morning in major cities, including in Atlanta, Chicago, Denver, Los Angeles, New York and Phoenix and across a swath of the Midwest.
According to the website Downdetector, which tracks user reports of internet disruptions, more than 104,000 cases of Verizon outages were reported across the country as of 11:30 a.m. Eastern, more than an hour after the first issues were reported.
By about noon, that number had dropped to around 78,000.
A map posted on the site showed areas with the most reports.
On the site, many users said their cellphones were intermittently displaying “SOS” mode and that they could not place calls or send or receive text messages.
“We’re aware of the issue affecting service for some customers,” a spokesman for Verizon, Ilya Hemlin, said in a telephone interview at 11:30 a.m.
“Our engineers are engaged and we are working quickly to solve the issue,” he added.
Mr. Hemlin said he had no information on the cause of the problem or whether it was linked to localized power failures in certain parts of the country.
He said the company would provide more information as soon as it was available.
On social media, where Verizon customers went to check if outages were widespread, Verizon technical support posted the same statement offered by the spokesman.
Throughout the morning, tech support responded individually to scores of users reporting issues.
Many people on X complained about how the outage would affect their ability to do jobs, such as deliver Instacart orders.
Verizon, one of the largest cellphone carriers in the world, has 114.2 million wireless subscribers in the United States.