Authorities say a wildfire has killed an Oklahoma truck driver in Kansas.

The Kansas Highway Patrol says 39-year-old Corey Holt, of Oklahoma City, jackknifed Monday while trying to back up his tractor-trailer on highway 34 in Clark County because of poor visibility and dust from the fires. The patrol says he succumbed to smoke when he got out of his vehicle.

Clark County, which is on Kansas’ southern border with Oklahoma, is the hardest hit by wildfires that have consumed an estimated 625 square miles in the state. State officials say 545 square miles of the burned land was in the county.

Wildfires are also burning in Colorado, Oklahoma and Texas, where a blaze killed three ranch hands on Monday.