Firefighters assess the scene as a house burns in the Napa wine region of California on October 9, 2017, as multiple wind-driven fires continue to ravage the area burning structures and causing widespread evacuations.

Firefighters in California will be tested by vicious winds on Friday morning as they battle a huge wildfire that has claimed the life of one of their colleagues and torched more than 700 homes.

Cory Iverson, 32, a California Department of Forestry and Fire Protection engineer, was killed on Thursday while tackling the so-called Thomas Fire in Ventura and Santa Barbara counties.

"Cory Iverson ... made the ultimate sacrifice to save the lives of others," said Ventura County Sheriff Geoff Dean during a community meeting on Thursday night.

Fire officials released little information about the circumstances surrounding Iverson's death. The Los Angeles Daily News reported that he perished in an accident near the community of Fillmore, where a mayday alert was sounded.

Santa Ana winds and humidity in the single digits has helped stoke the blaze that has swept through dry vegetation since it erupted on Dec. 4 near a small private college in Ojai. It has since blackened more than 249,000 acres (about 390 square miles, or 1,000 sq km) and is now the fourth-largest wildfire on record in California since 1932. On Friday morning powerful winds are forecast which will subside during the day, the National Weather Service said. "Winds will weaken Friday, turn westerly early Saturday, then become offshore and gusty again late Saturday night through Sunday evening," the service said in an advisory.

The wildfire remained a threat to some 18,000 homes and other structures in the communities of Santa Barbara, Carpinteria, Summerland and Montecito along California's coastline, especially if hot, dry Santa Ana winds return.

The Thomas Fire, which was 35 percent contained as of Thursday evening, has burned 729 homes to the ground and damaged another 175. The blaze has displaced more than 94,000 people.

The fire and others to the south in San Diego and Los Angeles counties have disrupted life for millions of people over the last 11 days.

They have caused schools to close for days, shut roads and driven hundreds of thousands from their homes and into shelters. The fires are also responsible for poor air quality throughout Southern California, forcing some commuters to wear protective face masks, local media reported.