Casper: An Australian bull rider has suffered life-threatening injuries when a bull threw him and stepped on his chest at the College National Finals Rodeo in Wyoming, his coach says.

Twenty-year-old Bradie Gray, from Hallsville, near Tamworth in northwestern NSW, suffered broken ribs, a bruised aorta and collapsed lungs Thursday night at the Casper Events Centre, Odessa College coach CJ Aragon told the Casper Star-Tribune.

Bradie Gray sustained serious injuries as a result of the incident. Credit:Alan Rogers

Gray had no pulse when he arrived at the Wyoming Medical Centre. He underwent surgery, was in a medically-induced coma and on a ventilator and faced another operation on Friday, Aragon said.

Gray was bucked off Frontier Rodeo's Levi the Boss and the bull stepped on his chest. He was able to stand up and was pulled into a bucking chute where he was put on a backboard and taken by ambulance to hospital.