Wildfires raging across the Southeastern United States have destroyed dozens of homes and prompted some communities to evacuate, officials said.

In southern Georgia, more than 27,000 acres of wildfires were blazing and evacuations were underway in several communities, according to the Georgia Forestry Association on Wednesday. Much of the state was under a burn ban.

“This is a serious and evolving situation,” said Tim Lowrimore, the forestry association’s president and chief executive.

Smoke spread across the Southeast and led to poor air quality from Atlanta to Jacksonville, Fla., and Columbia, S.C.

The National Weather Service office serving Atlanta reported that the air quality would be unhealthy for some people into at least Thursday and advised that children and people who are sensitive to ozone avoid prolonged outdoor exercise.

Gov. Brian Kemp of Georgia declared a state of emergency on Wednesday.

“With much of Georgia remaining in extreme drought conditions, wildfires have already surpassed the state’s five-year average and continue to spread,” he said.

In a social media post, the governor urged residents “to do your part in preventing the spread of wildfires as response teams work around the clock to contain those currently blazing.”

Sheriff Len Davis of Brantley County, in the state’s southeast corner, said during a news conference on Wednesday afternoon that wildfires had destroyed 54 homes and burned more than 5,000 acres.

As of 12 p.m. on Wednesday, about 25 people had moved into local shelters in Brantley County, Chuck White, the emergency manager for neighboring Camden County, said during a Wednesday afternoon news conference, but local officials are prepared for more.

One firefighter was treated on Tuesday for minor injuries, but has since been released, Sheriff Davis said. Joey Cason, the Brantley County manager, said during the news conference that it was a “miracle” that nobody had been seriously injured or killed.

The county has mobilized 22 fire departments from across South Georgia to combat the wildfire, Mr. Cason said.

Strong winds in the area on Wednesday have lowered the fire’s containment to about 10 percent, he added.

“This thing is a very dynamic situation that is changing in a matter of moments if the wind kicks in a certain way,” Mr. Cason said.

A drought in the Southeast United States has left the landscape parched and highly flammable. A single spark in the dry vegetation can turn into a rapidly spreading fire, especially with the light winds and low humidity that were prevalent on Wednesday.

“The ground is so dry,” said Tony Cruz, a meteorologist with the National Weather Service office in Jacksonville, Fla. “That’s the biggest factor right now.”

The U.S. Drought Monitor map tracks the intensity of drought by county across the country, and the highest levels used on the map, extreme to exceptional drought, were spread across north Florida and southern Georgia.

In Florida, the drought is the worst since the map was introduced in 2000, according to David Zierden, the Florida state climatologist at Florida State University. The state also had severe drought in 1998, when devastating wildfires broke out. The drought situation in Georgia is also severe.

North Florida and southern Georgia recorded below normal rainfall this winter, and since Oct. 1, the two regions have been experiencing rainfall deficits of 12 to 16 inches, Mr. Zierden said.

The hurricane season last year also brought below normal rainfall to the region because there were no storms that made landfall in the United States.

“Tropical rainfall in the late summer and fall is a critical part of our climatology and we missed that this year,” Mr. Zierden said.

With the ground extremely dry, the fires on Wednesday were burning under the surface, making them difficult to extinguish.

“Typically you have to rely on repeated rounds of heavy rain or sometimes you have to pump water into the ground,” said Andy Snyder, a fire meteorologist with the U.S. Wildland Fire Service in the Southeast.

The wildfire risk was expected to persist on Thursday with breezy winds in the forecast. Over the weekend, a chance for scattered thunderstorms could heighten the fire risk because lightning strikes can ignite new fires even as the storms bring rain.

“Typically thunderstorms are a worst-case scenario,” Mr. Snyder said. “It puts firefighters at risk, and it may impede the ability to fight fires with aircraft.”