Lightning sparked the fire in Virginia, officials said. It now involves 5,700 acres and is moving into the parkland in North Carolina, The Virginian-Pilot reported.
It's being fueled by dry conditions and dead trees left from Hurricane Isabel in 2003.
More than 140 firefighters from across the nation are battling it.
In Virginia, the Railroad Ditch Entrance and Lake Drummond are closed to public use because of the fires.
The entire Dismal Swamp State Park in North Carolina is closed.