Heavy thunderstorms soaked parts of the central United States for a fifth day yesterday as the region battled deadly floods that have driven hundreds from their homes.

Local media reports indicated as many as 12 people may have died directly or indirectly from the latest series of storms and resulting high water, including two adults and a child electrocuted in Wisconsin when lightning struck a utility poll at a bus stop in Madison on Wednesday.

Earlier, heavy rainfall in Texas and Oklahoma related to a tropical storm killed more than two dozen people.

The area around Findlay in northwest Ohio was among the hardest hit though the Blanchard River there was beginning to fall after cresting at near record levels, more than 2.1 metres above flood level.

But the National Weather Service issued a flash flood warning for counties in the area because thunderstorms continued to build.

In the Findlay area some residents were able to return home later yesterday to assess damage, the Ohio Emergency Management Agency said.

Nine Ohio counties have declared states of emergency.

"The flooding situation has worsened in Ottawa (west of Findlay). The flood levels rose another 30.4 cm overnight, and much of Findlay is still underwater at this hour since the waters are not receding very quickly," said Ohio EMA spokesman Tom Hunter. He said an elderly man in northern Ohio had died of smoke inhalation after flood waters tipped over a gasoline can, starting a fire from a pilot light. No other injuries were reported.

"Unfortunately, the weather forecast is still calling for chance of rain through much of the rest of the week but we are cautiously optimistic that the worst may be behind us in terms of the heaviest rainfall," Mr Hunter said.

Flood warnings were also posted in parts of Iowa, Illinois and Indiana following overnight storms that dumped from 2.5 cm to 12.5 cm of rain on already saturated areas. Forecasters warned of possible major flooding along the Des Moines River in the Fort Dodge area in northwest Iowa.