4-year-old killed by falling tree in Richmond, Va.

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RICHMOND, Va. (CNN) -- Powerful storms roared through the Mid-Atlantic states and portions of the Deep South, claiming the life of a child and knocking out power to hundreds of thousands of households.

At the peak of the outages, some 300,000 customers from Maryland to Georgia were without electricity, officials said.

The National Weather Service said a tornado was spotted near Colesville, Maryland, in suburban Washington.

In Richmond, Virginia, a 4-year-old child died and his father was injured when a tree fell on them Thursday afternoon, CNN affiliate WTVR reported.

The incident happened at Maymont, a 100-acre Victorian estate.

"The estate was being evacuated ... in preparation for the violent storm ... when the boy and an adult male with the boy were struck," said a post to Maymont's Facebook page. The estate will be closed until further notice.

As nightfall approached, storms with straight-line winds moved into the South and threatened the Atlanta metro area.

CNN affiliate WSB TV reported debris in the air and on the ground in suburbs to the northwest of the city.

WSB said winds as high as 70 mph swept through portions of Cobb County north of downtown Atlanta. It reported 900 lightning strikes in a span of 10 minutes in the area.

Widespread power outages

Officials in Maryland and Virginia said more than 134,000 customers had lost power. In Georgia, the number topped 170,000.

In Pennsylvania, the prestigious U.S. Open golf tournament resumed around noon after it was postponed because of severe weather moving into the area. And the weather situation appeared to be looking up for Philadelphia, near the site of the tournament. No severe weather is expected, and only light rain is in the forecast.

Earlier Thursday, with the words, "Turn around ... don't drown," the National Weather Service warned motorists in and around Lansing and Hastings, Michigan, not to drive through flooded streets.

Streets in Lansing were flooded and closed Thursday because of high water, according to CNN affiliate WILX.

The weather service warned that "only a few inches of rapidly flowing water can quickly carry away your vehicle."

Residents of Fort Wayne, Indiana, received a similar warning. "Flooding is occurring or is imminent," the service said.

CNN affiliate WANE reported Thursday that severe storms damaged northeast Indiana and northwest Ohio.

Damaging winds

A system of straight-line winds that slammed Chicago with 50-mph gusts and golf-ball-size hail Thursday bowled over trees and buildings in Auglaize, Ohio, CNN meteorologist Ivan Cabrera said.

The "derecho," as the windy system is called, usually builds in the Midwest then heads east, he said. "Derecho" is a Spanish word that means straight.

The system resembles a squall line, but instead of potentially producing tornadoes, it sends out a slicing wind.

Derechos usually dissipate quickly, but, Cabrera said, this one held together pretty good.

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