TUCSON, Ariz. — A wildfire that forced the evacuation of about 100 Arizona residents closed in on a heavily wooded area, leading firefighters to believe that the worst is yet to come.

The fire in the Coronado National Forest grew to 12,500 acres on Sunday as it threatened roughly 700 homes, said Joan Vasey, a spokeswoman for the forest. It hadn't damaged any structures, however.

"They are not too optimistic, even with all our resources, of being able to successfully deal with this fire," Vasey said. "The worst hasn't happened yet, but the potential is there."

The wildfire and extremely dry conditions also prompted officials to close to visitors the 222,000-acre forest district where the fire was burning.

Residents and business owners won't be allowed to return until after the fire threat is over, said Dean Barnella, chief of the Mount Lemmon Fire Department. "We are going door to door to confirm that everybody is out," he said.

Most of those evacuated were full-time residents. Many cabins on the mountainside are used as summer homes.

The fire was first spotted Tuesday and is believed to have been started by humans, authorities said.

In New Mexico, a wildfire burning in the rugged Pecos Wilderness of the Santa Fe National Forest had scorched 11,000 acres Sunday.

Firefighters had contained 15 percent of the blaze and were getting a break early Sunday as the wind died down.

Resident Ricky Romero watched the strong gusts fueling the blaze.

"I could see that fire coming straight at us so many times," Romero said, "and then the wind would change."

On the Net: National Interagency Fire Center: http://www.nifc.gov/