By Michael Fiala

CARMEL-BY-THE-SEA, Calif. (Reuters) - Firefighters struggled on Sunday to slow a deadly wildfire that has raged for 10 days near California's Big Sur coast, destroying dozens of homes and forcing the evacuation of hundreds of residents and campers, authorities said.

The so-called Soberanes Fire, which erupted on July 22 just south of Carmel-by-the-Sea, has grown to 40,000 acres (16,187 hectares) of parched chaparral and timberland in and around the Los Padres National Forest.

"Firefighters are meeting challenges due to topography, fuel load, and dry humidity," said Katherine Garver, a spokeswoman for the California Department of Forestry and Fire Protection (Cal Fire). "The fire is making runs into inaccessible areas."

Officials ordered evacuations for the famous Tassajara Zen Mountain Center in Pfeiffer Big Sur State Park and other areas on Sunday afternoon.

They had hoped that favorable weather conditions would allow progress to be made in containing the blaze, with strong winds that had been driving the fire for days starting to abate.

By Sunday night, 18 percent of the fire's perimeter was contained, a slight increase from earlier in the day, officials said.

Extremely hot, dry weather is still hampering the efforts of some 5,300 firefighters, 16 helicopters, a half dozen air tankers and 500 fire engines.

Officials do not expect the fire to be fully contained until the end of August because parts of it are burning in steep and inaccessible terrain. Its cause is under investigation.

Flames have already destroyed 57 homes and 11 outbuildings, with at least five other structures damaged, according to the latest tally. Another 2,000 structures were threatened, with an estimated 350 residents displaced by evacuations unrelated to those in the area of the Zen Center, officials said.

The fire threat has prompted authorities to close a string of popular California campgrounds and recreation areas along the northern end of the Big Sur coastline, including Point Lobos Natural Reserve.

The blaze took a deadly turn on Tuesday when a bulldozer operator hired by property owners to help battle the flames was killed when his tractor rolled over. It was the second California wildfire-related death in a week.

Another fire broke out on Saturday in grass and brush about 30 miles (48 km) northeast of Fresno, in central California, and has since spread to 1,500 acres (607 hectares), threatening 200 homes, according to Cal Fire.

(Writing and additional reporting by Frank McGurty in New York, Sharon Bernstein in Sacramento and Alex Dobuzinskis in Los Angeles, California; Editing by Sandra Maler, Paul Simao and Paul Tait)