A cellular phone outage hit cities across the US early on Thursday. Thousands of AT&T customers reported service disruptions that rendered them unable to send texts, access the internet or make calls, even to emergency services via 911. More than 50,000 incidents were reported at about 7am US eastern time, according to data from the outage tracking website Downdetector.com. Outage reports spiked above 70,000 around 9am eastern time. By 11am ET, reports of service failures had decreased to 60,000. Just after noon, AT&T said in a statement it had restored 75% of its network. Around 4pm ET, the company said it had “restored wireless service to all our affected customers”. “We sincerely apologize to them,” the company’s statement reads. An AT&T spokesperson, Jim Greer, said in an earlier statement: “Some of our customers are experiencing wireless service interruptions this morning. We are working urgently to restore service to them. We encourage the use of wifi calling until service is restored.” AT&T, the largest cellular service provider in the US, with 240 million subscribers, did not offer an explanation for the outage. The company also gave no timeline for when it expected full service to be restored. Intermittent outages have hit AT&T networks in recent days, but the scale of Thursday’s outage was much larger. Cities where most users were affected included San Francisco, Houston, Atlanta and Chicago, the website showed. Federal law enforcement agencies in the US were investigating whether a technical malfunction or a cyberattack could have caused the outage, ABC News reported. According to a memo from the Department of Homeland Security’s digital threats division, Cisa, “the cause of the outage is unknown and there are no indications of malicious activity.” Users of Verizon, T-Mobile, Cricket and UScellular also reported disruptions, though the outage with the services was much smaller than AT&T, according to Downdetector. Verizon and T-Mobile tweeted that the outage had not affected their own customers except when attempting to reach customers of another carrier. T-Mobile said in a statement: “We did not experience an outage.” Verizon’s statement read: “Verizon’s network is operating normally.” AT&T operates a network for first responders and emergency services, FirstNet, which went out alongside the company’s general cell network, but AT&T said FirstNet was back online by 10.30 am US eastern time. A post on the social media platform X, formerly Twitter, from the San Francisco fire department said the outage was affecting people’s ability to reach emergency services by dialing 911. “We are aware of an issue impacting AT&T wireless customers from making and receiving any phone calls (including to 911),” the fire department said, adding that it was “actively engaged and monitoring this”. Chicago’s office of emergency management and communications issued a similar statement. Atlanta’s mayor, Andre Dickens, said that calls to and from the city’s emergency services were still functional: “Atlanta’s e-911 is able to receive inbound and make outbound calls. We have received calls from AT&T customers that their cellular phones are in SOS mode.” Massachusetts state police said the department’s dispatch centers had been inundated with worried callers testing their phone service by dialing 911. The bureau advised against doing so. The department said via X: “Many 911 centers in the state are getting flooded w/ calls from people trying to see if 911 works from their cell phone. Please do not do this. If you can successfully place a non-emergency call to another number via your cell service then your 911 service will also work.”