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

It has burned 1.1 million acres north of the city of Amarillo - making it the second-largest fire in US history.

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

Dry grass, high temperatures and strong winds have fuelled the blaze, which remains 3% contained.

In Hutchinson County, one of the hardest-hit areas, public engagement coordinator Deidra Thomas told CNN one person had died in the blazes. The woman was identified by her family as 83-year-old Joyce Blankenship - a former substitute teacher.

The Smokehouse Creek Fire, as it has been named, has already razed 1.1 million acres - larger than the state of Rhode Island.

The West Odessa Fire Department said on Facebook that it "is now both the largest and most destructive fire in Texas History", surpassing the East Amarillo Complex fire, which burned over 900,000 acres in 2006.

The department also said it is now the second largest wildfire in US history.

There are five active wildfires in the state, according to the forest service, each burning tens of thousands acres, melting light posts and reducing buildings to a charred skeleton.

The Texas A&M Forest Service said that the winds had diminished slightly, helping to moderate the fire's spread.

Rain and cooler temperatures were 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 affected area, Seth Christensen, the spokesman for Texas Division of Emergency Management, said.

The Red Cross opened a disaster centre for one of the affected cities and said it would open another on Friday.

Governor Abbott also authorised additional state resources on Wednesday to extinguish the fires, including 94 firefighting personnel, 33 fire engines and six air tankers.

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.

The Potter County sheriff's office, which includes Amarillo, issued an announcement on Facebook on Wednesday, warning residents of the possibility of a mandatory evacuation.

"We will be knocking on your doors to let you know that you need to leave!" the message said in all-caps. "When it comes to that, there is no playing. Get a few things and get out."

More than 85% of cattle in the state are raised in the panhandle.

Hemphill County Emergency Management Coordinator Bill Kendall said he saw "hundreds of cattle just dead, laying in the fields".

One historic ranch in the state - the Turkey Track Ranch - said 80% of the 120-year old, 80,000 acre property has been damaged in the fire.

"The loss of livestock, crops, and wildlife, as well as ranch fencing and other infrastructure throughout our property as well as other ranches and homes across the region is, we believe, unparalleled in our history," the owners said in a statement.

In the affected area, more than 4,800 homes and businesses are without power, according to PowerOutage.us.

One Amarillo woman told The Texas Tribune she was in the kitchen preparing dinner when the smell of wildfire smoke crept in.

She was unharmed, but said her cousin in another nearby town was stuck somewhere where the highway exits were closed.

"I have a lot of family [in Fritch]. I had no clue if they're going to be OK," Brittany Struder said.

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".

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

In Oklahoma, just north of the state, over 30,000 acres have burned and at least 13 homes have been destroyed, according to the Oklahoma Department of Emergency Management.