Editor's Note: At 10:20 a.m., AT&T provided an update that said "three-quarters" of their network had been restored. Our original story continues below.
Some suburbs in the Chicago area are warning that residents have been unable to call 911 as thousands of AT&T customers are without power amid an outage.
"A systemwide outage is affecting AT&T and some other cellphone users, including the ability to call 911," the Lake County Sheriff's office posted on social media. "In case of an emergency, please attempt to use another phone with service or a landline until service providers can restore connectivity across the United States."
A spokesperson for the sheriff's office said many residents have been unable to reach emergency services.
Evanston police and fire officials noted that customers of AT&T, Verizon, Cricket and multiple other carriers may not be able to call 911 and urged residents to "utilize the text 911 feature" if possible.
The Chicago Office of Emergency Management and Communications confirmed to NBC Chicago that its 911 services had not been impacted by the outages, but urged customers not to test it.
"OEMC is aware of the issue impacting AT&T wireless customers from making and receiving calls (including to 911),"" Chicago's Office of Emergency Management and Communications said. "We are monitoring the situation closely and taking appropriate action."
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OMEC officials asked customer to not call 911 to test service.
"If you are an AT&T customer and unable get through to 911, try calling from a landline OR try to get ahold of a friend or family member who is a customer of a different carrier and ask them to call 911 on your behalf," OEMC said.
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Some AT&T customers reported to NBC Chicago that the message "SOS" in the upper right corner of their phone where service bars typically appear.
AT&T Thursday morning released a statement as more than 70,000 customers across the country reported cellular service outages.
“Some of our customers are experiencing wireless service interruptions this morning," AT&T said in a statement. "We are working urgently to restore service to them. We encourage the use of Wi-Fi calling until service is restored.”
As of 7:20 a.m., more than 70,000 AT&T outages were reported across the country.
According to the site's heatmap, the cities reporting the most outages were Los Angeles, Dallas, Indianapolis, Chicago, Houston, San Antonio, Louisville, Atlanta and Miami. As of 7:40 a.m., Downdetector reported 1,048 outages in the Chicago area.
"This heat map shows where user-submitted problem reports are concentrated over the past 24 hours," the site said, about the heatmap. "It is common for some problems to be reported throughout the day."
The website also showed Verizon and T-Mobile customers were also facing massive outages. As of 5 a.m., Downdetector showed more than 1,500 reports of Verizon outages, and nearly 700 T-Mobile outages.
A spokesman for Verizon told NBC News that they don't see any issues on their network and believes the problem is with other carriers. Verizon customers are only having issues when trying to call a number that is associated with one of the impacted carriers, the spokesperson said.
In an email to NBC Chicago, T-Mobile said their network was "operating normally," and that outages reported on Downdetector were likely reflecting T-Mobile customers attempting to reach users in other networks.
The Chicago area was't alone in warning of the impacts the outage has on 911 call centers.
"A cellular outage in the United States was reported by AT&T, T-Mobile, Verizon and other network users on Thursday," A tweet from the Cape Girardeau, Missouri Police Department said early Thursday, adding that the outage was impacting their phone system.
A similar tweet was sent by the Flager County Sheriff's Office in Northeast Florida.
This is a developing story that will be updated.
