Occupants of about 100 homes near Slide Rock State Park were advised to evacuate Tuesday afternoon, the U.S. Forest Service said. The Slide Fire was reported at about 4 p.m. in Oak Creek Canyon and by early Wednesday had charred about 850 acres.
Investigators said they believed the fire was started either accidentally or deliberately by human activity.
Capt. Bill Morse of the Flagstaff Fire Department said more than 20 Hotshot crews were either on the scene or on their way. Fire officials said that shifting winds made the fire's course difficult to predict.
Officials told KPHO-TV in Phoenix that, in a worst case scenario, the blaze could spread into Pumphouse Wash, a nearby valley, on a course that would take it north towards Flagstaff and the nearby communities of Kachina Village and Mountainaire. A 2-mile area north of the state park was evacuated as a precaution.
The American Red Cross set up an evacuation center in Flagstaff while the Human Society provided shelter for pets.