AT&T said on Thursday that it had fully restored service to its wireless network after a widespread outage temporarily cut off connections for users across the United States for many hours, the cause of which was still under investigation.
The outage, which affected people in cities including Atlanta, Los Angeles and New York, was first reported around 3:30 a.m. Eastern time, according to Downdetector.com, which tracks user reports of telecommunication and internet disruptions. At its peak, the site listed around 70,000 reports of disrupted service for the wireless carrier.
Multiple government agencies said they were looking into the incident, although the Biden administration told reporters that AT&T said there was no reason to think it was a cyberattack.
AT&T did not disclose the scope of the outage, nor the reason for it. When the outage first began on Thursday morning, the company listed the cause as “maintenance activity.”
Jim Greer, an AT&T spokesman, apologized in a statement confirming service was restored and said the company was “taking steps to ensure our customers do not experience this again in the future.”
The outage underscored the importance of connectivity to daily life as individuals and businesses were cut off from communications and the ability to use mobile apps. AT&T advised consumers they could make calls over Wi-Fi and sought to respond to angry customers online. Many phones showed an “SOS” symbol on their screen, signaling they could only make emergency calls, while local governments offered alternate ways to reach 911.
Reports of outages on Downdetector began to fall midmorning, and at one point AT&T’s website showed that outages were limited to users in California, though users in other states were still reporting issues. Cricket, which is owned by AT&T, also reported that its users were experiencing wireless service interruptions and said it was working to restore service.
Reports also surfaced early Thursday that FirstNet, the network AT&T maintains for emergency services personnel, had experienced outages, but AT&T said around 10:30 a.m. that the network was fully operational.
Verizon experienced 3,000 reports of outages at one point on Thursday and T-Mobile about half that. Both companies said in statements that their networks were operating normally.
“Some customers experienced issues this morning when calling or texting with customers served by another carrier,” Verizon said. “We are continuing to monitor the situation.”
In an email, T-Mobile said that it did not experience an outage. “Downdetector is likely reflecting challenges our customers were having attempting to connect to users on other networks.”
Officials in Washington said they were working to understand the cause of the outage. A spokesman for the Federal Communications Commission said its inquiry was being handled by its Public Safety and Homeland Security Bureau, which was in touch with AT&T as well as other providers.
John Kirby, a National Security Council spokesman, said on a call with reporters on Thursday that the Biden administration was told “that AT&T has no reason to think this was a cybersecurity incident,” although he added that they would not be certain until an investigation had been completed.
Mr. Kirby said that, in addition to the F.C.C., the Department of Homeland Security and the F.B.I. were collaborating with technology companies to investigate the outage.
The F.B.I. said in a statement it was in touch with AT&T and would respond accordingly if any malicious activity was found.
Throughout the day, cities urged residents to find alternate ways of reaching emergency or municipal services, like landlines or phones connected to Wi-Fi. The City of Upper Arlington, Ohio, said the fire department might not be notified of fire alarms because of the outage. It urged that any fire alarm be followed up with a 911 call.
The San Francisco Fire Department said on social media that it was aware of an issue affecting AT&T users who were trying to call 911. “We are actively engaged and monitoring this,” the fire department said. “If you are an AT&T customer and cannot get through to 911, then please try calling from a landline.”
The Massachusetts State Police said on social media on Thursday morning that 911 call centers across the state had been flooded with calls from people checking to see if the emergency service worked from their phones. “Please do not do this,” the police said. “If you can successfully place a non-emergency call to another number via your cell service then your 911 service will also work.”
Even in less extreme circumstances, the outage complicated the many elements of life that have come to rely on a reliable connection to the internet.
Staff at the First Watch restaurant in Dania Beach, Fla., had to turn away breakfast customers for a time while the outage prevented them from processing payments.
Debra Maddow, who lives in southwest Houston, said that she first noticed something was off after 7 a.m., when she went to check traffic and Google Maps was offline. Later, she visited a Starbucks to make an urgent call through its free Wi-Fi, she said.
“I’m really frustrated that they’re not telling us anything,” Ms. Maddow said in a phone interview over Wi-Fi. She said she tried to call AT&T for an update, but after a long time on hold, the call was dropped.
Victor Mather, John Keefe, Zolan Kanno-Youngs and Adam Goldman contributed reporting.
