An unknown number of homes and other structures in Hutchinson County were damaged or destroyed, local emergency officials said.
The main facility that assembles and disassembles America's nuclear arsenal shut down its operations Tuesday night.
"We have evacuated our personnel, non-essential personnel from the site, just in an abundance of caution," Laef Pendergraft, a spokesman for National Nuclear Security Administration's Production Office at Pantex, said during a news conference.
"But we do have a well-equipped fire department that has trained for these scenarios, that is on-site and watching and ready should any kind of real emergency arise on the plant site."
Early on Wednesday Pantex posted on X that the plant "is open for normal day shift operations" and all personnel were to report for duty according to their assigned schedule.
Since 1975 Pantex has been the US main assembly and disassembly site for its atomic bombs.
It assembled the last new bomb in 1991 while disassembling thousands.
Republican Governor Greg Abbott issued a disaster declaration for 60 counties as the largest blaze, the Smokehouse Creek Fire, burned more than 1000 square kilometres, according to the Texas A&M Forest Service.
That is more than twice its size since the fire sparked on Monday.
Authorities have not said what might have caused the blaze, which tore through sparsely populated counties surrounded by rolling plains.
"Texans are urged to limit activities that could create sparks and take precautions to keep their loved ones safe," Abbott said.
The weather forecast provided some hope for firefighters: cooler temperatures, less wind and possibly rain on Thursday. But for now, the situation was dire in some areas.
Multiple fires were reported across Hemphill and Hutchinson counties near the Oklahoma border, where some evacuations were ordered along with school closures.
Fire officials across the border in the area of Durham, Oklahoma, also encouraged people to evacuate because of the fire.
