PHOENIX (Reuters) - Firefighters struggled on Wednesday to slow the advance of a fast-growing wildfire threatening thousands of structures in central Arizona and forcing evacuations of residents from at least a dozen communities, authorities said.

The so-called Goodwin Fire, roaring through dense, sun-baked chaparral, has destroyed a number of homes in an area close to where flames erupted on Saturday in the Prescott National Forest, about 70 miles north of Phoenix.

But the full extent of property losses has yet to be determined because of continued fierce fire activity in the vicinity, said Tiffany Davila, a spokeswoman for the state Department of Forestry and Fire.

“We know there’s losses back in there, but we don’t know how bad it is,” she told Reuters.

As of Wednesday, the wind-whipped blaze had charred 21,000 acres, while firefighters have managed to carve containment lines around just 1 percent of the perimeter.

A force of about 1,000 fire personnel, backed by airplane tankers dumping payloads of flame-retardant chemicals, focused on trying to safeguard the most heavily populated areas lying in harm’s way on the northeastern fringe of the blaze, Davila said.

Yavapai County spokesman David McAtee said an estimated 3,000 homes and other buildings were under threat, with evacuations expanded to cover the entire town of Mayer, parts of Dewey-Humboldt and at least 10 other communities or subdivisions.

Mayer alone is home to about 1,400 residents, and Davila said as many as 3,000 people in all were believed to be under evacuation orders or advisories warning them to be prepared to flee at a moment’s notice.

Governor Doug Ducey issued state of emergency for Yavapai County, freeing up extra funds to help fight the blaze there.

Davila said Goodwin was the most severe of 35 wildfires burning across Arizona on Wednesday, from smaller, isolated blazes to a 60-square-mile conflagration in the southeastern corner of the state reported to be 43 percent contained.

The National Interagency Fire Center in Boise, Idaho, reported nearly 30 “active large” fires in Arizona and eight other Western states on Wednesday that have engulfed nearly 180,000 acres.

Heavy rainfall in parts of the West over the winter and spring helped delay the onset of wildfires, but spurred the growth of dense vegetation that has now dried out and was fueling fire activity as summertime heat sets in.

In the neighboring state of Utah, another fierce wildfire that has destroyed more than a dozen homes and forced the evacuation of 1,500 residents raged for a 12th day on Wednesday about 300 miles (483 km) south of Salt Lake City. That fire has scorched more than 54,000 acres (21,853 hectares), an increase of about 4,000 acres since Tuesday.

In California, several smaller wildfires were burning on Wednesday, including a new blaze threatening hillside homes in the Los Angeles suburb of Burbank, and the so-called Hill Fire along the state’s central coast that destroyed the home of “The Big Bang Theory” actor Johnny Galecki and two other structures.