The twister barrelled over the town of Dayton late Monday, damaging homes and uprooting trees. No deaths have been reported so far.
The National Weather Service said the tornado cut electricity supplies to five million people and parts of the state faced the risk of flash flooding in the wake of the storm.
"We have lost power to both water plants and pump stations. First Responders are performing search and rescue operations and debris clearing," the official account for the city of Dayton tweeted.
Emergency workers were shutting down gas lines and trying to get to residents trapped by debris, officials in Montgomery County said.
The exact injury toll was unclear from initial reports.
The tornado was the third in a week to rake the central US.
At least two people died and another 29 were hospitalised in Oklahoma over the weekend when a tornado flattened a mobile home park in El Reno.
President Donald Trump, who was returning to Washington on Tuesday after a visit to Japan, tweeted that he had offered federal resources for the cleanup.
Another three died last Wednesday when a tornado packing speeds of 260 kilometers per hour tore through Jefferson City in Missouri.