AT&T is experiencing a major outage, beginning 4am Eastern.

Users at Verizon, T-Mobile, Boost Mobile, Consumer Cellular, UScellular, and Straight Talk have all reported issues - but it appears that they are just unable to call AT&T subscribers.

911 operators have warned that the outage has hampered their ability to take calls.

"AT&T has reported that some calls to 9-1-1 may not be received by the County's Public Safety Communications Center," Prince William County said in an alert. "If you are calling 9-1-1 to report an emergency and your call is not answered, please call the County's non-emergency line."

The issue seems to be across the US and Canada, with users on social media coming from New York, Boston, Washington, Montreal, Honolulu, Atlanta, Houston, Dallas, Los Angeles, Seattle, and San Francisco.

AT&T said that it is "working urgently" to restore service. "We encourage the use of Wi-Fi calling until service is restored," it added.

Kentik director of Internet analysis Doug Madory said on X: "The fact that today’s AT&T outage affected some devices and not others (sometimes within a single household) suggests this isn’t BGP (or solar flares, cyberwar, etc.), but some sort of faulty maintenance push by AT&T."

Update: As of 10:15am CT, "three-quarters of our network has been restored," AT&T said.

We will update this story as we learn more.