Massive clouds of smoke choked Flagstaff on Tuesday as firefighters battled to keep a nearly 19-square-mile wildfire from heading toward the mountain town of about 60,000 people.

The work shifted after firefighters secured the area closest to homes, several hundred of which remained under evacuation orders, said fire spokeswoman Erin Phelps. Crews will work on containment lines on the south and north sides where the fire is most active, she said.

The fire is about five miles from Flagstaff on the southernmost edge where rocky terrain and rolling hills could make the terrain more difficult for fire crews to access.