Dec. 11 (UPI) -- The Thomas Fire, the largest of the blazes burning across Southern California, is now more than 350 square miles -- and firefighters are still struggling to get it under control, authorities said.
Officials said the fire in Santa Barbara County has so far burned more 230,000 acres as it moves westward. It has destroyed about 800 structures, damaged 200 and threatens another 18,000.
Authorities say the Thomas Fire has forced nearly 100,000 evacuations or sheltering of residents. Nearly 6,000 firefighting personnel are engaged with the blaze, which continues spreading, Cal Fire said -- adding that 762 fire engines, 30 helicopters, 60 bulldozers and 41 water tenders have been pressed into service.
Schools in Santa Barbara and Ventura Counties remain closed and several districts ended their semesters until the new year. UC Santa Barbara announced that the university will postpone final exams until next year.
Utility Southern California Edison reported that up to 85,000 customers in Santa Barbara County are without power due to the flames.
Officials said the fire, which began a week ago, grew by 50,000 acres Sunday and was aided by 35 mph winds and low humidity, the Los Angeles Times reported. Of particular concern is the town of Carpinteria, where six structures burned Sunday -- a community surrounded by thick, dry vegetation that hasn't burned in 100 years.
"The fuels in there are thick and they're dead so they're very receptive to fire," said Steve Swindle, Ventura County Fire Department spokesman.
The Thomas Fire is now regarded as the fifth-largest in state history.
While fire officials were initially optimistic about containing the blaze, they were more cautionary Sunday in their predictions, the Santa Barbara Independent reported. At a community meeting, Santa Barbara County Sheriff Bill Brown called the fire "menacing" and "rapidly moving," adding, "This is not going to end tonight or tomorrow."
Airborne ash is spreading throughout the area, much of which is invisible. Experts recommended that people leave the area, if only for several hours.
Firefighters made progress over the weekend in containing other fires in Southern California.
In Los Angeles County, the Creek Fire was 90 percent contained by the end of the weekend; the Rye Fire was 90 percent contained and the Skirball Fire was 75 percent contained. In San Diego County, the Lilac fire was at 60 percent containment after burning through 4,100 acres -- although officials cautioned that swirling Santa could cause embers to start new fires.
An activist organization said thousands of farm workers in Ventura County have worked during the past week in smoky conditions and without protective face masks. As air quality deteriorated, over 70,000 free face masks were donated to workers by aid organization Direct Relief. They were distributed throughout Santa Barbara County, but a similar offer was never made in Ventura County, Lucas Zucker of the Central Coast Alliance for a Sustainable Economy said. He added that many farm owners refused to shut down operations as air quality reached unhealthy levels, despite advisories from Ventura County agriculture officials to do so.