A rapidly spreading Texas wildfire has forced residents to evacuate, cut off power to homes and businesses and briefly paused operations at a nuclear weapons facility.

The second largest fire in Texas history, it has burned 500,000 acres of land north of the city of Amarillo.

Texas Governor Greg Abbott issued a disaster declaration for 60 counties.

Dry grass, high temperatures and strong winds have fuelled the conflagration.

The Texas A&M Forest Service said that the winds had diminished slightly, helping to moderate the fire's spread. It remained 0% contained as of Wednesday morning, however.

Rain was expected in the state's northern panhandle on Thursday, which may aid efforts to extinguish the blaze.

In the meantime, hundreds of firefighters and first responders have been deployed to the fire, Seth Christensen, the spokesman for Texas Division of Emergency Management, said.

The Smokehouse Creek Fire, as it has been named, has already razed half a million acres. It remains behind the East Amarillo Complex fire, which burned over 900,000 acres in 2006.

The Smokehouse Creek Fire has caused several towns, a neighbourhood in the city of Amarillo, and other communities to evacuate, according to the forest service and local law enforcement.

The National Weather Service has warned residents near Amarillo to remain indoors with their pets because of the poor air quality. Texas has issued warnings to farmers about the potential impact on agriculture and livestock.

In the affected area, more than 4,500 homes and businesses are without power, according to PowerOutage.us.

Concerns about the spreading fire north of the Pantex nuclear weapons site in Amarillo forced the facility to temporarily close and evacuate staff on Tuesday night. The plant is a key site for the assembly, dismantlement and maintenance of US nuclear weapons.

Pantex said on Facebook that it reopened on Wednesday morning, as there was no fire within the plant site.

Laef Pendergraft, a nuclear safety engineer at the National Nuclear Security Administration production office at Pantex, told a news conference on Tuesday night that an emergency response team had been activated.

He added that the plant's own fire department "has trained for these scenarios".

The forest service said it was wrestling with other fires in Texas as well.

Unexpected high temperatures have led to wildfires in nearby states, including Nebraska and Kansas. (BBC)

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