McALLEN, Texas (AP) — Strong winds spread flames on Sunday and prompted at least one evacuation while airplanes dropped fire retardant over the northern Texas Panhandle as firefighters worked to stop the largest wildfire in state history.

As of Sunday afternoon, the Smokehouse Creek fire, which has burned more than 1 million acres (404,685 hectares), was 15% contained. Two other fires that have burned a combined 180,000 acres (72,843 hectares), were 60% contained.

Authorities have not said what ignited the fires, but strong winds, dry grass and unseasonably warm temperatures fed the blazes.

A cluster of fires has burned across more than 1,900 square miles (4,921 square kilometers) in rural areas surrounding Amarillo, while the largest blaze spilled into neighboring Oklahoma.

U.S. Homeland Security Secretary Alejandro Mayorkas on Sunday said the federal government has devoted funds, equipment and personnel to assist with battling the fires, but warned more extreme weather could be coming.

“More than a million acres have burned. And we are in winter, and this is the largest fire in Texas history,” Mayorkas said during a CNN interview. “We, as a country and as a world, have to be ready for the increasing effects of extreme weather caused by climate change. It’s a remarkable phenomenon, and it will manifest itself in the days to come, and we have to prepare for it now.”

The National Weather Service on Sunday issued red flag warnings — signifying extreme fire risk due to warm temperatures, low humidity and strong winds — across much of the central U.S., including Texas and its neighboring states of New Mexico and Oklahoma.

Red flag warnings also covered nearly all of Nebraska and Iowa, along with large swaths of Kansas, Missouri and South Dakota. Smaller portions of Colorado, Wyoming, Minnesota and Illinois also were under red flag warnings.

Strong winds spread the flames, prompting an evacuation order to be issued in Sanford, a Texas town of a little more than 100 residents, according to a post by the Amarillo office of the National Weather Service on X, formerly Twitter.

As firefighters fought the unprecedented wildfires, humanitarian organizations pivoted to victims who have lost their homes and livelihoods. Residents began clearing affected property on Saturday and by Sunday the extent of the loss began mounting.

Donations ranging from $25 to $500 have been critical for the Hutchinson County United Way Wildfire Relief Fund, which is dispersing proceeds to displaced families.

“We already know that a large group of people are uninsured who lost their homes. So without monetary assistance, it’s going to be very hard for them to start back over,” said Julie Winters, executive director for Hutchinson County United Way.

The organization has heard estimates of more than 150 homes being impacted in the county, noting the fires extend to at least five other counties, Winters said.

A steady outpouring of donated clothing, water and hot meals quickly overwhelmed one community in the affected area. The city of Borger, Texas, urged people in a social media post to redirect donation efforts from food and water to clean-up supplies including shovels, rakes, gloves and trash bags.

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Associated Press writer Thomas Strong in Washington, D.C., and Trisha Ahmed in Minneapolis contributed to this story.