The department said the aluminum-covered, dome-shaped balloon is 20 feet long and 5 feet high.
The Federal Aviation Administration is trying to track the aircraft on radar and has notified the Denver International Airport. Shortly after noon (2 p.m. ET), the balloon was sighted two miles south of Evans.
CNN meteorologist Chad Myers estimated the wind would keep the vessel moving at 30 mph. Authorities say the craft is about 7,000 feet above the ground.
Kathy Davis, spokeswoman for the sheriff's department, said a dispatcher received a call Thursday morning, and emergency services personnel were contacted.
Davis said a balloon company had been contacted and several media outlets offered to help track the balloon with their helicopters.
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