Authorities warned about 3,200 residents between Sedona and Flagstaff that they need to be ready to evacuate if the fire makes another advance. The blaze earlier Wednesday doubled in size to 1 1/3 square miles and could grow by nightfall to 2,000 acres, or about 3 square miles.
Arizona authorities are fearful that the fire could be a prelude for what could become a devastating wildfire season amid a drought that has left tinder-dry conditions across the state.
The fire broke out at the start of the tourist season and closed the main road between Sedona and Flagstaff - two cities that attract many visitors in summer months. The fire is burning near Slide Rock State Park, a popular recreation area because of its natural rock water slides.
Sophie Lwin, of Peoria, said she had relatives from the Los Angeles area coming in for a weekend at the Butterfly Garden Inn, which had to evacuate because of the fire. She said the area is her favorite destination, and she and her husband visit the Sedona area at least five times a year.
"It's Memorial Day weekend. It's going to be so hard and so expensive to get anything anywhere else," she said.
About 200 firefighters and other personnel are already assigned to the fire, including five Hotshot crews, Coconino National Forest officials said Wednesday. An additional 15 Hotshot crews are on order, as well as 10 other firefighting crews and dozens of fire engines, officials said. A top-level fire management team was taking over command of the fire.
There were no reports so far of injuries or structures burned. The exact cause of the fire wasn't known, but authorities believe it was human-caused.
The fire forced the evacuations of 100 threatened businesses and homes in a 2-mile stretch north of the state park, and 15 people stayed at a shelter in Flagstaff. About 3,200 people in the communities of Kachina Village and Forest Highlands were told that they need to be ready to evacuate.
"As you can see, we are dealing with some pretty extraordinary circumstances with this fire. I want to reiterate that you basically have received your pre-evacuation notice. This is your time to get ready," said Robert Rowley, emergency manager for Coconino County.
The fire comes less than a year after a blaze in nearby Prescott killed 19 firefighters who were part of a Hotshot crew.
As the fire moved up the canyon's steep walls, it sent up large amounts of smoke and ash and created hazy conditions in Flagstaff, about 10 miles from the blaze.
The blaze presented several challenges for firefighters, including steep terrain, thick pine forest, gusting winds and the drought conditions, said Bill Morse, a Flagstaff Fire Department captain and a spokesman for firefighting managers. He also said the terrain makes it difficult for firefighters to stay in contact with each other on their radios.
But Morse said calming fire conditions in Southern California have freed up extra crews to fight the Arizona fire.
"Fortunately the fires in San Diego have calmed down enough for the resources to be released here," Morse said.
The evacuees included Nathan and Mickella Westerfield, young honeymooners from Phoenix who arrived at a campground in the canyon Tuesday afternoon. They were headed into Sedona for dinner when they passed the fire, which was burning shrubs and trees in a small valley visible from the highway.
As other passers-by stopped to take pictures of the fire, a firefighter told the couple they couldn't return to their campground to retrieve their newly purchased camping gear and other belongings, Nathan Westerfield said.
"He told us, 'no, we're evacuating,'" he said. "We literally have the clothes on our backs."
Red Cross spokeswoman Trudy Thompson Rice said most of the 15 people who stayed Tuesday night at the shelter at a Flagstaff school were campers. The Westerfields were among those who spent the night at the shelter.
A separate wildfire burned 200 acres and closed Interstate 17 near Cordes Junction in both directions for more than four hours late Tuesday. The interstate, which is the main route between the Phoenix area and northern Arizona, reopened Tuesday evening.
Davenport and Associated Press writer Astrid Galvan contributed to this report from Phoenix.