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The Federal Communications Commission is investigating a brief but an apparently nationwide outage of 911 service for customers of AT&T, its chairman said Wednesday night.

A spokesperson for AT&T confirmed to NBC News late Wednesday that the company encountered a "service issue" that affected "some calls to 911 for wireless customers." A few minutes later, the company tweeted that service had been restored for all customers.

Issue has been resolved that affected some calls to 911 from wireless customers. We apologize to those who were affected. — AT&T (@ATT) March 9, 2017

The company didn't say how widespread the outage was, but as reports poured in from across the country, Karima Holmes, director of unified communications for the Washington, D.C., government, said her office had been "advised there is a nationwide outage for AT&T."

We have been advised there is a nationwide outage for AT&T – for 911 AT&T customers should call 202-373-3700 ext 2. — OUC Director (@OUCDirector) March 9, 2017

Ajit Pai, chairman of the Federal Communications Commission, said the agency was already investigating.

We're receiving reports of widespread AT&T 911 call outages. @FCC public safety staff are investigating. I'll post more info once available. — Ajit Pai (@AjitPaiFCC) March 9, 2017

At 10:20 p.m. ET, about 10 minutes before AT&T gave the all-clear, DownDetector, a site that monitors internet traffic for real-time information on wireless and broadband carriers, indicated that outage reports for AT&T were clustered most prominently around New York City, Philadelphia, Washington, D.C., Chicago, Miami, Dallas, Houston, San Francisco, Los Angeles and Seattle.

At 10:20 p.m. ET, the web monitoring site DownDetector indicating heavy reports of AT&T wireless outages in many U.S. metropolitan areas. DownDetector.com

But emergency authorities across the country confirmed 911 outages and publicized direct police, fire and ambulance dispatch telephone numbers that AT&T customers should call in emergencies.

AT&T mobile cell service outage across TN. Impacting ability to dial 911. AT&T customers use landline in emergency or call 615-862-8600. — Metro Nashville PD (@MNPDNashville) March 9, 2017

URGENT: @ATT customers may experience trouble connecting with E-911. Lexington residents with AT&T should call 859-258-3600 in an emergency. — Lexington Police (@lexkypolice) March 9, 2017

AT&T is reporting issues for some customers when dialing 911. Kanawha County residents please call 304-348-8111 to receive 911 assistance. — Amanda Barren (@amandabarren) March 9, 2017