The outage, triggered by cut fiber lines, brought down internet, television and phone service for Comcast XFINITY customers in markets including NY and Philadelphia.
"It is now affecting our business and residential internet, video and voice customers", the company wrote on Twitter midday Friday.
Comcast, one of the dominant telecom companies in the USA with more than 29 million business and residential customers, said on social media that it was working to restore services to affected customers.
The outage began about 1 p.m. ET on Friday.
On Twitter, Comcast has told customers they are "working to restore service". "We again apologize to anyone who was impacted".
Comcast, one of America's largest internet service providers, relies on network partners to deliver its services across the country.
There's no official word from Comcast on when a resolution is expected.
We'll update this story as Comcast comes back online or if the outage continues or worsens throughout the day.