CenturyLink's status page notes the issue, caused by a "network element" problem, started at around noon Eastern Time on Thursday. The company is working to resolve the problem, and service has been restored in some areas, such as Massachusetts.
CenturyLink provides cell services to several carriers, including AT&T and Verizon -- the outage didn't impact emergency calls from landlines. Residents in some affected areas received alerts to inform them of the problem. The notifications often indicated alternate means to contact emergency services if necessary.
The Federal Communications Commission is looking into the situation, with chairman Ajit Pai saying the outage is "completely unacceptable, and its breadth and duration are particularly troubling."
"I've directed the Public Safety and Homeland Security Bureau to immediately launch an investigation into the cause and impact of this outage. This inquiry will include an examination of the effect that CenturyLink's outage appears to have had on other providers' 911 services," he said in a statement.
CenturyLink could face penalties over the incident. In June, the FCC reached a settlement with AT&T that saw the company pay a $5.25 million fine and establish additional systems to reduce the risk of 911 outages. Two incidents last year that lasted 5 hours and 45 minutes respectively stopped thousands of 911 calls from going through on the provider's network.