The flames were so intense that firefighters had to fall back from their positions, according to Larry Helmerick, spokesman for the U.S. Forest Service's Rocky Mountain Area Coordination Center.
The wind, meanwhile, kept grounded tanker planes and two helicopters that were available to fight the blaze, which was in a mixture of timber, sage and grass.
``We've had estimates that could get into well over 1,000 acres, but right now it's very preliminary,'' Helmerick said. ``But we know it's going to be a large fire.''
A Crook County dispatcher confirmed the information. She and Helmerick were unsure what buildings were at risk but both said protective measures were being taken.
The fire was near the South Dakota line in east-central Crook County.
Helmerick said the area was under a red-flag warning due to warm, dry weather and wind, and had been considered ripe for a large wildfire.