New York (AFP) - Time Warner Cable apologized for a "very serious failure" after millions of people across the United States were knocked off the Internet because of a fault.

An estimated 11 million Internet subscribers were hit by the early morning outage on Wednesday, which lasted more than hour, The Wall Street Journal said, while other reports said the problem affected customers nationwide.

"During an overnight network maintenance activity in which we were managing IP addresses, an erroneous configuration was propagated throughout our national backbone, resulting in a network outage," the company said in a statement.

"We immediately identified and corrected the root cause of the issue and restored service by 7:30 am ET (Eastern Time).

"We apologize for any inconvenience this caused our customers. A failure of this size is very serious and we are taking the necessary steps to improve our processes with the objective of making sure this doesn’t happen again."

The outage comes days after federal regulators fined Time Warner Cable for inadequate reporting of some outages in 2013, the WSJ said.

The firm also said on Twitter that services had been restored, although some people were still reporting their Internet was down hours after the announcement.