(CNN Money) — Comcast customers across the United States experienced a massive internet, cable TV, and telephone outage on Friday.

The outage started Friday morning and quickly spread to several cities, including New York, Philadelphia, Atlanta, San Francisco, Denver and Chicago, according to Downdetector.com, a site that monitors service outages. Complaints peaked early in the day, but Comcast outages continued popping up well into the afternoon.

Comcast was scrambling to determine just what went wrong, but said in a statement that “one of Comcast’s large backbone network partners had a fiber cut that we believe is also impacting other providers.”

The company could not say how long it might take to rectify the problem, which it called “nationwide.”

Fiber optic cables are used for long distance high-speed data transmission.

Customers took to their cellphones and mobile devices to complain vociferously on Twitter. Some reported difficulty getting through to Comcast customer service. The company took to Twitter to provide updates and urge customers not to call 911.


© Copyright 2018 CNN. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.