Update 10:15 p.m.
The fire jumped the Little Big Horn River near Dunsmore, but Tracy Spang, BIA acting fire management officer for Crow Agency, says crews have that part of the fire controlled.
At the northern part of the fire, crews have about 30 percent containment, according to Big Horn County Fire Chief Matt Redden.
Update 4:15 p.m.
A Type II Incident Management Team is expected to arrive at the Poverty Flats Fire on Thursday morning to evaluate the blaze.
John Kohn, BIA fire information officer, said the fire is currently being managed by the Big Horn County Rural Fire Department with assistance from state and federal resources.
Fire crews are working to protect structures in the small community of Dunmore, Kohn said. Crews are also working to prevent the blaze from moving south and east.
Kohn said the fire spread quickly after it started Tuesday afternoon about 10 miles north of Hardin. It reached the reservation at about 1 a.m. Thursday, he said.
Update 3:15 p.m.
A spokesman for Red Cross said the emergency shelter in Crow Agency is serving 21 people who have evacuated due to the wildfire.
Update: 2:45 p.m.
A revised estimate of the fire Wednesday afternoon puts the blaze at 75,000 acres but growing fast, according to Tracy Spang of the BIA.
A wildfire burning in Big Horn County has grown to 100,000 acres, a fire official said Wednesday.
The Poverty Flats Fire started Tuesday around 1:30 p.m. near the Sarpy Creek Road. The fire jumped Highway 384 heading toward Crow Agency and traveled south toward the Little Bighorn River and the community of Dunmore.
In the Dunmore area on the west side of the river structures were being threatened but no evacuations have been ordered.
According to Tracy Spang of the BIA Forestry and Wildland Fire Management in Crow Agency, the fire is burning around 100,000 acres with zero containment.
On the Crow Agency side around 20 firefighters are on scene and other local ranch crews are helping with heavy equipment.
A helicopter crew was also helping to fight the blaze.
The Montana Red Cross has set up an emergency shelter in Crow Agency for residents displaced by the fire. The shelter is located at the Crow Tribal Multi-Purpose Building, 178 Multi-Purpose Road in Crow Agency.