A firefighter battling the Smokehouse Creek Fire, near Amarillo, in the Texas Panhandle AFP

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

The Texas A&M Forest Service said five major fires, fueled by winter heat 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.

The forest service said it was confident weather conditions would help firefighters' efforts on Thursday.

"The fire environment will be cooler today across the Texas Panhandle where multiple large fires are established. Fire activity today will not be as resistant to suppression efforts compared to Monday and Tuesday," it said in a statement.

In addition to the five ongoing blazes, another 18 fires across the north and east of Texas have already largely been contained, officials said.

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, Deidra Thomas, told ABC News.

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

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

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.