AUSTIN, Texas (Reuters) - Fast-moving wildfires that burned through nearly 2 million acres (809,380 hectares) of Texas, Oklahoma and Kansas this week have devastated ranches and left thousands of cattle and other livestock dead, officials said on Thursday.

Many of the grass fires grew rapidly on Monday due to dry weather and parched prairie land in the Texas Panhandle, north and western Oklahoma and southern Kansas. Several of the blazes were largely contained on Thursday as hundreds have battled the blazes on the ground and in the air.

Six people have been killed in the fires, including three ranch hands in Texas who died trying to protect cattle from oncoming flames. The fires in Kansas were the largest recorded, at about 631,000 total acres (255,350 hectares), state officials said.

Many ranchers have not yet been able to return to their land but those who did have seen the loss of herds and destruction of fencing, officials said.

“Unfortunately, it (cattle loss) has been in the thousands, but there is not a specific number on the amount of cattle that have been killed,” Katie Horner, an emergency management spokeswoman in No.3 cattle state Kansas, said in a social media post.

In Texas, the top U.S. cattle producer, losses were also expected to be large, officials said.

The losses are not having an impact on cattle futures or prices of cattle ready for slaughter. Texas has 12.3 million head of cattle, followed by 6.45 million in Nebraska and 6.4 million in Kansas, according to U.S. cattle inventory data.

Two wildfires that burned through about 164,000 acres (66,370 hectares) in the Texas Panhandle were 100 percent contained on Thursday, and the largest blaze, the so-called Perryton fire of about 318,000 acres, was 75 percent contained, according to the Texas A&M Forest Service.

The Perryton fire is the third-largest recorded in Texas, it added.

The National Weather Service canceled a critical fire risk warning for the Texas Panhandle into Oklahoma, Kansas and western Missouri it had issued on Wednesday, saying a weak low pressure front was in the area, bringing moisture to the air.

In Oklahoma, two ranches in Woodward County lost about 200 head of cattle total and a hog farm operation lost several thousand animals in the wildfires, Luke Kanclerz, spokesman for the Oklahoma Forestry Services said. He added the number will climb when the fires are and damage can assessed in other places.