Emergency crews have struggled to contain deadly wildfires in four US states which have killed at least four people and forced thousands of others to flee their homes.
The fires are burning in parts of Kansas, Oklahoma, Texas and Colorado, with warnings over spreading flames issued for Iowa, Missouri and Nebraska.
Powerful thunderstorms had moved through the nation's midsection overnight, spawning dozens of tornadoes, according to the National Weather Service.
In Kansas, wildfires have burned about 625 square miles of land and killed one person.
The Kansas Highway Patrol said tractor-trailer driver Corey Holt, of Oklahoma City, was killed on Monday when his rig jackknifed as he tried to backup because of poor visibility on highway 34 in Clark County, which is on Kansas' southern border with Oklahoma. He succumbed to smoke inhalation after getting out of his vehicle.
About 545 square miles of the state's burned land is in Clark County, where 30 structures have been damaged, including some homes, said Allison Kuhns, a spokeswoman for the county's emergency management office.
She said about half of the structures were damaged in or near the small city of Englewood, which was among two in the county that was evacuated. Ms Kuhns said there also have been significant cattle losses and that entire ranches had been engulfed.
The largest evacuations were in Reno County, where 10,000 to 12,000 people voluntarily left their homes on Monday night. A total of 66 people from the area were in shelters on Tuesday in Hutchinson, 40 miles north-west of Wichita.
Several hundred more people evacuated their homes in Russell, Ellsworth and Comanche counties, which are in central Kansas.
The Kansas fires forced the closure of some roads, including two short stretches of Interstate 70 in the central part of the state. A stretch of the US 54 road in southern Kansas's Pratt County also was closed because of smoke from a fire near a cotton gin and surrounding grassland.
In the Texas Panhandle, a pair of fires burned more than 195 square miles. One of the blazes near Amarillo threatened about 150 homes, while a larger fire in the north-east corner of the Panhandle near the Oklahoma border was only 5% contained as of Tuesday morning.
A wildfire in Gray County, which is also in the Texas Panhandle, killed three ranch hands who were trying to usher cattle away from the flames, said Judge Richard Peet, the county's head administrator.
One of the three apparently died of smoke inhalation on Monday night and the other two were badly burned and died on the way to hospitals.
Forest Service spokesman Phillip Truitt said as many as four firefighters were hurt battling the fires.
In north-eastern Colorado near the Nebraska border, firefighters lost ground to a blaze in rural Logan and Phillips counties.
They had the blaze 90% contained on Monday evening, but only 50% contained on Tuesday, despite working overnight to douse hot spots and flare-ups.
The fire has burned more than 45 square miles of land and destroyed three homes. Nearby residents were warned to be ready to evacuate if the fire advances.
More than 70 firefighters from 13 departments battled the blaze, which was reported east of Sterling on Monday morning. The fire, which was driven by wind gusts of nearly 50mph, jumped Interstate 76 and spread into Phillips County.