Fire crews along with local engines and air support are battling the Cyr Gulch Creek Fire, reported around 1 p.m. Wednesday.
It is burning about 5 miles due south of Frenchtown on private timber land in the Deep Creek area, in an area between Bear Gulch and Cyr Gulch, north of Deep Creek Road and west of the Clark Fork River.
At last report, the fire is burning an estimated 20 acres with no containment at this time. The blaze is wind-driven and making some runs up north slopes. Fire officials report it is exhibiting "very active fire behavior with torching and spotting."
A second fire to the south was also detected Wednesday, and crews are also working to fight it.
Crews anticipate working through the night and Thursday at the site of the blaze.
The fire is producing smoke visible from Missoula and the surrounding area.
No structures are threatened at this time.
Officials are asking people to stay away from the Deep Creek area as crews work to control the blaze.