A nuclear weapons plant in the US state of Texas said it would be open as usual on Wednesday after pausing operations due to wildfires in the area.

"The Pantex Plant is open for normal day shift operations for Wednesday, February 28; all personnel are to report for duty according to their assigned schedule," plant operators said in a post on X, formerly Twitter.

The Texas A&M Forest Service reported early Wednesday that 25 of 31 fires raging in the state were under control, but the largest blaze -- known as the Smokehouse Creek Fire -- had burnt 300,000 acres and remained uncontained.

Satellite imagery showed fires spreading near the northern city of Amarillo, fanned by strong winds and unseasonably warm temperatures, according to the local office of the National Weather Service.

The Pantex plant, located 21 miles (34 kilometres) from Amarillo, had earlier announced it was halting operations and had constructed a fire barrier to protect its facilities.

"Operations at the Pantex Plant have paused until further notice. All weapons and special materials are safe and unaffected," it said on Tuesday evening.

The Pantex facility in Texas assembles and disassembles the United States' nuclear stockpiles, carries out special nuclear material testing and manufactures high explosives.

Texas governor Greg Abbott issued a disaster declaration for 60 counties on Tuesday, freeing up fire response resources.

"Texans are urged to limit activities that could create sparks and take precautions to keep their loved ones safe," Abbott said in a statement.

Amarillo's weather service warned people to stay indoors.

"Air quality remains poor in the Amarillo area... as smoke continues to stream southward," it said in a post on X.

Several towns, some up to 100 miles (160 kilometres) from Amarillo, issued evacuation orders, closing roads and ordering citizens to take shelter at home or in public facilities.