HUTCHINSON, Kan. — Crews grappling with vexing wildfires that have charred hundreds of square miles of land in four states and killed six people soon may get a bit of a break: Winds are forecast to ease from the gusts that have whipped the flames.

Bill Bunting, forecast operations chief for the Oklahoma-based Storm Prediction Center, said the powerful wind gusts that have helped the wildfires spread quickly in Kansas, Colorado, Oklahoma and Texas should die down to about 10 to 20 mph Wednesday. He said temperatures should top off in the 70s, with humidity low.

“These conditions will make it somewhat easier for firefighting efforts, but far from perfect. The fires still will be moving,” Bunting said. “The ideal situation is that it would turn cold and rain, and unfortunately that’s not going to happen.”

Fires raged in parts of Kansas, Oklahoma, Texas and Colorado, and warnings that conditions were ripe were issued for Iowa, Missouri and Nebraska. The fire warning came after powerful thunderstorms moved through the middle of the country overnight, spawning tornadoes, according to the National Weather Service.

Kansas wildfires have burned about 625 square miles of land and killed one person.

The Kansas Highway Patrol said Corey Holt, of Oklahoma City, died Monday when his tractor-trailer jackknifed as he tried to back up because of poor visibility on a southern Kansas highway, and he succumbed to smoke after getting out of his vehicle.

Two SUVs crashed into the truck, injuring six people who were taken to hospitals, state trooper Michael Racy said.

The largest evacuations elsewhere were in Reno County, Kan., where 10,000 to 12,000 people voluntarily left their homes Monday night, said Katie Horner, a spokeswoman for the state’s Department of Emergency Management. She said 66 people from the area were in shelters Tuesday in Hutchinson, 40 miles northwest of Wichita.

In the Texas Panhandle, three fires have burned about 500 square miles of land and killed at least four people.

One of the blazes in the northeast corner of the Panhandle near the Oklahoma border was 50 percent contained, according to Texas A&M Forest Service. That fire was responsible for a death Monday, authorities said Tuesday.

A wildfire in Gray County, 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.

Forest Service spokesman Phillip Truitt said as many as four firefighters were hurt Monday.

In northeastern Colorado, firefighters were battling a blaze that had burned more than 45 square miles and was 50 percent contained Tuesday. Officials said the fire had destroyed five homes and 15 outbuildings.