Large swathes of the U.S. were hit by a cellular outage early on Thursday, with thousands of users reporting disruptions with the services offered by telecom firms including AT&T.

More than 32,000 outage incidents were reported with AT&T’s service around 4:30 a.m. ET, according to data from outage tracking website Downdetector.com. Impacted cities included San Francisco, Houston and Chicago, the website showed.

Users of Verizon, T-Mobile and UScellular also reported issues with the telecom firms’ services, according to Downdetector.

The companies did not immediately respond to Reuters requests for comment on the reason behind the outages.

A post on social media platform X from the San Francisco Fire Department said the outage was impacting 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 on the platform formerly known as Twitter, adding that it was “actively engaged and monitoring this.”

A News10NBC staff member experienced an outage on Thursday morning.