As the stubborn blaze entered its sixth day, it was transitioning "from a wind-driven fire to a topography-driven fire," according to the Ventura County Fire Department. Powerful Santa Ana winds and low humidity helped the fire spread quickly during its early stages.
The fire, which began Monday in Santa Paula, has destroyed 710 structures and damaged 118 others. Some 15,000 structures remain threatened.
RELATED: List of evacuations, school and road closures in Ventura County amid Thomas Fire
Mandatory evacuation orders remained in effect for areas including La Conchita, Casitas Springs, and some unincorporated areas of Ventura County and Matilija Canyon.
More than 4,400 personnel are involved in the firefight, supported by water-dropping helicopters and fixed-wing aircraft. Among the deployed planes was a DC-10 that was seen making dramatic drops of fire retardant.
The cost of fighting the Thomas Fire reached $17 million, fire officials said.
California Gov. Jerry Brown on Saturday toured Ventura County neighborhoods ravaged by a weeklong wildfire that killed at least one person.
He said deadly and destructive wildfires in the winter are "the new normal."
At a news conference, Brown said drought and climate change mean California faces a "new reality" where lives and property are continually threatened by fire, at a cost of billions of dollars.
He added that gusty winds and low humidity are continuing and warned that there's a good chance of seeing "firefighting at Christmas."
He said it will take "heroic" efforts in the U.S. and abroad to stem climate change and urged U.S. lawmakers to pay more attention to dealing with natural disasters such as fires, floods and earthquakes.
The Associated Press contributed to this report.