In Roane County in West Virginia, police were struggling to close roads after flooding shut down the 911 center, The Charleston Gazette reported. Police urged everyone to avoid driving and said some highways would be closed until further notice.
"We've had a lot of water rescues that we can't get to, so what the 911 center has asked me to do is close the traffic off so no one else gets through," John Kelley of the Walton Volunteer Fire Department told the Gazette.
The county north of Charleston was the only place in the state with significant storm damage, officials said, although downed trees were reported in other areas. Gov. Earl Ray Tomblin declared a state of emergency and said an emergency shelter was opening at the Roane County National Guard Armory.
Play at the U.S. Open, held this year at the Merion Golf Club 11 miles west of Philadelphia, was suspended during the morning because of bad weather, CNN reported. It resumed around noon.
A 57-mph wind gust was recorded midmorning in Woodbury, N.J., while emergency managers in Frederick County, Md., reported multiple incidents of downed trees, Accuweather.com reported.
The system of massive thunderstorms and hailstorms with severely damaging winds spawned at least two tornadoes near Columbus, Ohio, late Wednesday night. No injuries were immediately reported.
About 9:15 a.m., Webster County, W.Va., reported receiving more than 1.5 inches of rain in less than two hours.
Earlier, the U.S. Open suspended play as storms approached Philadelphia. Elsewhere in Pennsylvania, three homes were reported to have sustained minor damage from a lightning strike. Minor road flooding was reported throughout the area.
Hail ranging from quarter-size to that of ping-pong balls was reported in two counties in Maryland.
The strong thunderstorms brought a high risk of flash flooding to West Virginia, Virginia, the District of Columbia, Maryland, Pennsylvania, New Jersey and New York through most of Thursday, with flooding also possible in North Carolina, South Carolina and northeast Georgia, the National Weather Service and AccuWeather said.
The weather service had previously issued tornado and severe-thunderstorm warnings for other Ohio Valley counties and points east and southeast after the unusually massive line of storms plowed through eastern Iowa, northern Illinois and Indiana and southeast Michigan.
At least one tornado was reported in north-central Iowa about 90 miles north of Des Moines.
More than a dozen homes and businesses were reported damaged by winds gusting to nearly 50 mph in Iowa, and power was reported out in many areas of Iowa, Illinois, Indiana, Ohio and western Pennsylvania.
Northeast Ohio was under a flood watch through Thursday afternoon.
Airlines canceled more than 150 flights at O'Hare International Airport in Chicago.