New evacuation orders were issued on Saturday in Santa Barbara County, California, as wind gusts up to 60mph pushed the third-largest wildfire in state history towards a wealthy enclave which is home to Oprah Winfrey and other celebrities.

The mandatory evacuation zone was increased to 17 miles long and up to five miles wide, extending from coastal mountains north-west of Los Angeles to the ocean.

One firefighter was killed on Thursday. The Ventura County medical examiner announced autopsy results on Saturday for Cory Iverson, 32, who died from burns and smoke inhalation on the eastern flank of the Thomas blaze, in canyons near the agricultural town of Fillmore. No other details were released.

Iverson’s death was a stunning blow to those fighting the flames.

“When that happened, this fire hit a whole new level because all the firefighters know that could have been them,” said Steve Concialdi of the Orange County Fire Authority. “When you lose a fellow brother, that hits all of us and our families extremely hard.”

The fire was also was blamed for the death last week of a 70-year-old woman who died in a car crash on an evacuation route.

The Thomas fire began on 4 December in Santa Paula and has burned a record acreage, officials said on Saturday. Concialdi said the Thomas fire had burned 2,000 acres more than the devastating Rim Fire of 2013.

“As of this morning, we’re at 259,000 acres and still growing,” Concialdi said.

The region has had “red flag” or hot, dry and windy conditions for an unprecedented 13 consecutive days. The National Weather Service (NWS) said those conditions would last at least through Saturday evening.

Santa Barbara has had only a tiny amount of rain since 1 October, the start of the new water year, and is more than 3in (7.6cm) below normal to date.

Everything about the fire is massive, from a footprint larger than that of many cities to the sheer scale of destruction that has cremated entire neighborhoods to the legions attacking it. About 8,300 firefighters from nearly a dozen states have been aided by 78 bulldozers and 29 helicopters dropping thousands of gallons of water. Firefighting costs are approaching $89m.

The fire in Ventura and Santa Barbara counties has burned more than 1,000 buildings, including more than 750 homes. Another 18,000 buildings are still in jeopardy, including mansions in the wealthy enclave of Montecito.

Some 315 fire engines were stationed in and around homes in Montecito and Santa Barbara on Saturday, along with “hand crews” armed with equipment like chain saws and drop torches. Another 200 fire engines were on standby. Concialdi said authorities were hoping to have the blaze contained by 7 January.