Firefighters worked through the night trying to contain wind-driven wildfires that raced across hundreds of thousands of acres on the dry southern Plains, forcing the evacuation of several small towns and killing at least seven people.
More than 660,000 acres had been blackened by Monday morning in Texas.
Fields near Interstate 40 in Gray and Donley counties were ablaze, and fallen trees smoldered in roadside ravines. Blackened rolling hills could be seen for miles.
At least one highway was closed in the area because utility poles had burned at their bases and the lines sagged over the roadway.
The burned acreage -- more than 1,000 square miles or about two-thirds the size of Rhode Island -- far eclipsed the deadly wildfires in December and January that prompted Gov. Rick Perry to declare a statewide drought disaster. Those blazes charred more than 455,000 acres, destroyed more than 340 homes and killed three people.
"This is probably one of the biggest fire days in Texas history," said Warren Bielenberg, a spokesman for the Texas Forest Service.
Officials weren't certain what sparked the string of wildfires, but wind gusting up to 55 mph and low humidity made conditions ideal for fires to spread. The parched region around Amarillo has had just three-tenths of an inch of rain since February, nearly an inch below normal, and no rain is expected for at least another week.
Cooler temperatures Monday should help firefighters, but wind was expected to keep blowing at around 15 mph, meteorologists said.
In southeastern New Mexico, 100,000 acres of tinder-dry grass and brush had burned by Monday morning, forcing the evacuation of up to 200 people in two communities, authorities said. Flames damaged a post office and several other buildings in McDonald, officials said. One person suffered burns.
Four people died in a chain-reaction crash on Interstate 40 east of Groom as smoke obscured the road. Three others died in fires near Borger, northeast of Amarillo.
Bill Tidwell worked overnight in his hometown of Alanreed to fight spot fires with his shovel.
"It's burning houses down all over the country," said Tidwell, 68. "I've never seen nothing like it."
Wildfires forced residents to evacuate eight small towns over the weekend, although some were allowed to return to Skellytown and Lefors late Sunday.
Eight to 10 structures were destroyed near Borger, about 40 miles northeast of Amarillo, Galloway said. Firefighters worked through the night to try to contain the blazes.
Two people near Borger died trying to escape a grass fire that consumed their home, fire Capt. Mike Galloway said.
"The brush fire overtook their house and yard and got them," he said. "The flames just spread so fast."
Another person died in Hutchinson County, said Sheriff's Deputy Aaron McWilliams.
Volunteer firefighter Danny Whittington said 15 to 20 structures were lost in a fire between Pampa and McLean.
"I've seen something I've never seen before and that's cattle and horses burned. You'd think they would run, but they just stood there," Whittington told the Amarillo Globe-News.
Low visibility in dense smoke forced officials to close an 89-mile stretch of Interstate 40 from Amarillo to Shamrock for six hours Sunday, said Daniel Hawthorne, a spokesman for the Department of Public Safety.
Shamrock City Manager John Rhodes said a few hundred people, including some elderly and sick patients from nursing homes, were transported in school buses. Some of the nursing home residents were later moved to other facilities.