NEW YORK >> Time Warner Cable said Wednesday that service was largely restored after a problem during routine maintenance caused a nationwide outage of its Internet service for hours.

The company said it is still investigating the cause of the problem, which occurred with its Internet backbone — the paths that local or regional networks connect to in order to carry data long distances.

The problem affected all of Time Warner Cable’s markets and started at 4:30 a.m. Eastern, sparking widespread complaints on social networks. Service was largely restored by 6 a.m. The company is working to bring all customers back online.

Time Warner Cable, which is in the process of being bought by rival Comcast Corp. for $45 billion, has about 11.4 million high-speed data subscribers in 29 states. The Federal Communications Commission is reviewing the deal.

The New York State Department of Public Service will investigate the outage as part of its review of Comcast’s proposed merger with New York-based Time Warner Cable, said New York Governor Andrew Cuomo in a Wednesday statement.

There are major outages of at least one telecom provider every year, although typically they aren’t national, said Tim Farrar, an analyst at TMF Associates.

“AT&T had a major outage back in April, Comcast had one last October. Verizon Wireless had several national outages on its 4G network back in 2012,” he said. “Usually it is related to bugs in new technology, and occasionally to routine maintenance where someone did something wrong.”

Separately, on Tuesday, the FCC said Time Warner Cable would pay $1.1 million to resolve outage reporting violations. The FCC found that Time Warner Cable did not report disruptions in service to its networks to the FCC in a timely manner. In addition to the payment, the company is submitting a three-year plan to make sure it will comply with the reporting rules.

Time Warner Cable shares rose 64 cents to $147.23 during midday trading.