By Scott DiSavino

Aug 13 (Reuters) - Power supply was cut on Thursday to about 450,000 homes and businesses across the U.S. Midwest as severe storms battered the region, data from PowerOutage.us showed.

Indiana was the hardest-hit state, with more than 234,495 outages, representing about 7% of its roughly 3.3 million customers, the data showed.

"Rounds of severe thunderstorms will threaten the plains, midwest and east into Thursday with damaging wind gusts, while repeated downpours could trigger dangerous flash flooding," weather forecaster AccuWeather said in a statement.

Indiana's hardest-hit utility was Northern Indiana Public Service Co, taking out services to about 230,637 homes and businesses, or about 49% of its roughly 468,000 customers in the state. NIPSCO is a unit of Indiana energy firm NiSource ( NI ).

In a statement, the utility said it was assessing damage and would provide estimated restoration times when the task was complete, but warned that restoration could take days in some areas as the damage was extensive.

"There is widespread damage to electric infrastructure, including downed poles, power lines, and trees," it added.

Duke Energy ( DUK ) said that after the storms left widespread outages, crews had made considerable progress making repairs and assessing the damage left behind.

It expects to restore power to most of its more than 37,000 customers in Greater Cincinnati in Ohio, who are experiencing outages, by 11:59 p.m. CET tonight, though it noted many cases may be resolved sooner.

It added that this was the latest time for restoration the company anticipates keeping in mind the majority of customers already restored, with more than 171,000 customers having been without power over the past 24 hours across the Greater Cincinnati area.

About 34,700 homes and businesses were without power, or about 5% of its roughly 768,281 customers in Ohio.

Other energy firms with power outages include units of Exelon ( EXC ), and American Electric Power Co. ( AEP )

Here are the major outages by state:

State Outages

Indiana 234,495

Illinois 89,581

Ohio 69,666

California 14,099

Kentucky 12,284

Total Out 484,032