The fire was reported shortly after 10:15 a.m. at the Dallas Fairgrounds.
"Big Tex was done in about 10 minutes," Allen Ferrell, who was visiting the fair with a church group from North Richland Hills, told The Dallas Morning News.
The giant cowboy statue had welcomed visitors since 1952.
"It's a very sad day for all fairgoers. It's a sad way to end the fair," fair spokeswoman Sue Gooding said, adding no one was in danger at any time.
"Big things happen in Dallas, and Big Tex was a symbol of that. I'm sure we'll rebuild him and make him better than ever for the 21st century," Mayor Mike Rawlings said upon arriving at the fairgrounds to inspect the damage. "Everyone is so emotional about this. I guess I thought I'd pay my respects to Big Tex."
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