Flagstaff, Ariz. ? Firefighters in aircraft and on the ground battled the second serious wildfire to threaten buildings in two days Sunday as officials urged hundreds of residents to flee their homes and a huge plume of smoke spread over parts of this forested mountain city.

The fast-spreading fire erupted in Flagstaff’s northern outskirts early Sunday and grew to more than 7 square miles in size by evening, fire officials said.

Residents of hundreds of homes were urged to evacuate because of the blaze, dubbed the Shultz fire, city spokeswoman Kimberly Ott said.

Some heeded the call but it was unclear how many; others watched as bright red and orange flames climbed over a mountain behind a cloud of towering smoke.

The blaze was within 500 yards of a scattering of homes beneath the mountain, spurring firefighters to work feverishly on a containment line, said fire spokesman Eric Neitzel

Four helicopters and eight air tankers dropped fire suppression chemicals and 300 firefighters battled the blaze, and more crews were on the way, Ott said.

U.S. 89 north of this northern Arizona city of about 60,000 was closed because of smoke from the Shultz fire. Its cause was unknown.

Also Sunday, evacuation orders for a fire that emerged Saturday in southeastern Flagstaff were lifted after officials reported it 25 percent contained.