Texas emergency crews were struggling Thursday to contain the largest wildfire in the US state's history, with the blaze killing at least two people and scorching a million acres as it raged out of control.

The Texas A&M Forest Service said five major fires, fueled by an unseasonably hot winter and ferocious winds, were actively burning across the state's northern area known as the Texas panhandle.

The largest, the Smokehouse Creek Fire, started on Monday, grew to a record 1,075,000 acres (435,000 hectares) in size, and was just three percent contained, the forest service said.

With Smokehouse Creek merging with another blaze, it has now become the state's largest-ever wildfire, surpassing the East Amarillo Complex disaster that torched 907,000 acres in 2006.

A 44-year-old truck driver died in an Oklahoma City hospital on Thursday, having been rescued near her smoke-engulfed truck in Smokehouse Creek on Tuesday, according to several local media, citing a Texas public safety department official.

While preventive evacuations were ordered across multiple localities, the body of an 83-year-old woman was found in the city of Stinnett, a Hutchinson County emergency services spokesperson told ABC News.

She also said about 20 structures in Stinnett had been razed by the fire.

A 120-year-old Texas ranch said it lost 80 percent of its 32,000-acre property near the area of the largest 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 managers of Turkey Track Ranch said in a statement posted on its website.

Governor Greg Abbott on Tuesday issued a disaster declaration for 60 Texas counties, a move that frees up resources to battle the fires.

President Joe Biden, while visiting the southern border, told reporters that 500 federal personnel were working on fire suppression in Texas.

"I directed my team to do everything possible to help protect the people in the communities threatened by these fires," Biden said, promising federal support to Texas and neighboring Oklahoma while also slamming those who deny climate change.

"I love some of my Neanderthal friends who still think there's no climate change," he said.

Cities across the United States and Canada saw record temperatures in February, with some experiencing summer-like heat. An El Nino weather pattern is at play, in addition to climate change, according to experts.