UPDATE: As of 6:30 p.m. fire officials say evacuations from 21 residences have been completed and no structure damage has been reported.
Crews have started a burnout in the area to try and contain the blaze, and the fire is expected to expand rapidly above its estimated 700 acres.
Officials say there is some concern the blaze could eventually spread to the east side of the canyon in East Missoula.
SEATs and heavy tanker are working the fire with retardant, and the Lolo Hot Shots are on the ground.
A Type II response team will be briefed on the fire tomorrow at 9 a.m.
The cause of the blaze is still under investigation.
Lake County Public Information Officer Karen Sargeant has confirmed for NBC Montana that evacuations are underway in the Jocko Canyon area of Arlee. It is not known at this time how many structures are threatened, and the investigation is in preliminary stages. The fire is being referred to by authorities as the "Firestone Flats Fire."
According to the Forest Service, by 5:00 p.m. Saturday the fire had burned an estimated 700 acres. Officials report the Lolo Hotshots are currently working the fire. And the Seeley Lake Ranger Dist. is closing a portion of Jocko Rd. for safety.
Sergeant says Search and Rescue is heading to the area to help with evacuations, and Arlee Fire and DNRC is responding as well.
Authorities say the fire is burning in the south side of the canyon. Two engines and two dozers have been taken off the Mill Creek Fire burning near Frenchtown, and were dispatched to the fire in Arlee.
NBC Montana has a crew on the way, and will update this article as more information becomes available.