Rapidly moving Texas wildfires have prompted evacuation orders in small towns and shut down a nuclear facility as strong winds, dry grass and unseasonably warm temperatures fuelled the blaze in the state’s rural Panhandle.

Republican governor Greg Abbott issued a disaster declaration for 60 counties on Tuesday as the largest fire burned nearly 400 square miles, 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,” Mr Abbott said.

The largest blaze, known as the Smokehouse Creek fire, closed highways and remained uncontained as of Tuesday afternoon, according to the forest service.

The main facility that assembles and disassembles America’s nuclear arsenal shut down its operations on Tuesday night in Texas as fires raged out of control near its facility.

Pantex issued a statement online saying it had paused operations until further notice.

“The fire near Pantex is not contained,” the company said. “Response efforts have shifted to evacuations. There is a small number of non-essential personnel sheltered on-site.”

Since 1975, Pantex has been the US’ main assembly and disassembly site for its atomic bombs. It assembled the last new bomb in 1991. In the time since, it has dismantled thousands of weapons.

Pantex is located 30 miles east of Amarillo.

Multiple fires were reported across Hemphill and Hutchinson counties near the Oklahoma border, where some evacuations were also ordered.

Texas state senator Kevin Sparks said an evacuation order was issued for the town of Canadian, about 100 miles northeast of Amarillo, and other areas.

Later on Tuesday, the Hemphill County sheriff’s office urged anyone who remained in Canadian to shelter in place or at the high school gym because roads were closed.

Evacuations were also ordered in nearby Miami, and schools in Canadian and Miami announced closures on Wednesday.

East of Canadian, fire officials across the border in the area of Durham, Oklahoma, also encouraged people to evacuate because of the fire.

Evacuations were also taking place in Skellytown, Wheeler, Allison and Briscoe, according to the National Weather Service in Amarillo.

About 40 miles southwest of Canadian, city officials in Pampa on Facebook suggested that residents evacuate to the south and said buses were available for that purpose. Officials said personnel were still fighting the fire on Tuesday night but that residents of Pampa could return home.

“They were able to get the fire stopped north of town,” weather service officials said on X, formerly known as Twitter.

To the west, at least some residents in the small city of Fritch in Hutchinson County were told to leave their homes on Tuesday afternoon because of another fire that had jumped a highway.

“Everything south of Highway 146 in Fritch evacuate now!” city officials said on Facebook.

Officials with Hutchinson County emergency management and in the nearby city of Borger, which had also been evacuated, posted on Tuesday night on Facebook places where evacuees could shelter in both cities.

They said so many fires were burning in the county that it was “extremely hard” to keep everyone on the same page while they respond on the front lines.