Firefighters battle 2 growing wildfires near Flagstaff, Arizona

Two wildfires are threatening communities near Flagstaff, Arizona, as the fire danger remains high due to dry, hot conditions.

The largest, the Pipeline Fire, has quickly swelled to over 20,100 acres since first reported on Sunday and is 0% contained. It is burning about 6 miles north of Flagstaff, with "critical" weather concerns due to warm and windy conditions, according to the National Interagency Coordination Center.

The Haywire Fire is also burning nearby, about 17 miles northeast of Flagstaff. It has grown to over 4,000 acres since first reported on Monday and merged with the smaller Double Fire and is also 0% contained.

On Monday, the Coconino County Board of Supervisors declared a state of emergency due to the Pipeline and Haywire fires.

Several communities are under evacuation and parts of the Coconino National Forest are temporarily closed due to the fires.

High winds and remote terrain have challenged the fire response, though aerial operations were seen on Tuesday. Some 500 fire personnel are working on both fires, with aerial resources including six helicopters and one fixed-wing aircraft, state officials said Tuesday.

"We are priority for all our aircraft, at least in the region if not the nation," Aaron Graeser, incident commander for the U.S. Forest Service, told reporters Monday.

The causes of both fires are under investigation. Fire officials suspect a lightning strike caused the Haywire Fire. A 57-year-old man was arrested by U.S. Forest Service law enforcement officers for "federal natural resource violations" in connection with the Pipeline Fire, according to the Coconino County Sheriff's Office.

Federal court records show Matthew Riser was charged with building a prohibited fire, residing on national forest lands and possession of a controlled substance (marijuana).

Riser allegedly lit toilet paper on fire in the Coconino National Forest around noon on Saturday. The Pipeline Fire was reported the following day at around 10:30 a.m. in the area, according to a statement of probable cause. Riser reportedly told a law enforcement officer that he did not see the "no campfire" signs, but saw them when he drove out of the area, the probable cause stated.

His attorney told Phoenix ABC affiliate KNXV there is no evidence that Riser started the fire. A detention hearing is scheduled for Thursday.