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The fires that spread this week during an extreme drought in Georgia and Florida have blanketed cities hundreds of miles away in smoke, leading to more air quality warnings Thursday across the Southeast.

Driven by strong winds and low humidity, the two biggest fires in southern Georgia have spread rapidly over the past two days and destroyed more than 50 homes in rural areas. But the growing threat led to more evacuations and school closings on Wednesday.

"I don't know if I have a house standing or not," said Denise Stephens, who was forced to evacuate because of the fast-moving Brantley County fire near Georgia's coast. "I know what it's taken from other people, but I don't know what I have left standing."

The Brantley County fire, which has caused much of the structural damage, remained stable overnight, the sheriff's office said Thursday.

"While this stability is encouraging, wind conditions remain unpredictable and could cause conditions to change rapidly," according to the update, which said the blaze is about 15% contained.

WATCH: Why firefighters are facing toxic smoke with little to no protection

It was not known yet how the wildfires started, but the bottom half of Georgia and northern Florida are both extremely dry.

The National Weather Service warned drivers in southeastern Georgia early Thursday that visibility could be down to a one-half mile on some highways as smoke from the wildfires moved across the area.

Visibility was especially poor in Clinch and Echols counties — near the Pineland Road fire, the state's biggest, the weather service said.

In Florida, firefighters were battling more than 130 wildfires, mostly in the state's northern half. Those have been smaller than the fires to the north.

Associated Press reporter Jeff Martin in Atlanta contributed.