Spokeswoman Terri Nisich told the Associated Press that firefighters had begun an aggressive operation from dawn on Friday, using nine water-dropping helicopters to try to quell the flames.
Santa Barbara County's fire chief Ron Prince said: "We're going to have a very, very tough day today for firefighting and when the winds kick up this afternoon, we're going to have an incredibly challenging situation."
"Control of this fire is not even in sight," he said on Friday morning.
The speed of the fire's spread late on Thursday - fuelled by gusts of wind of to 70mph (113km/h) - took people by surprise.
Actor Rob Lowe told Oprah Winfrey on her chat show that he and his family had fled from their home as the flames suddenly closed in.
They both said their homes had so far escaped the fire.
California Governor Arnold Schwarzenegger declared a state of emergency for Santa Barbara County, giving local firefighters additional state resources.
By early Friday the flames had reached the outskirts of nearby Santa Barbara city, but officials said it remained unclear how many homes had been damaged.
Many of the homes at risk in Montecito, which has long been a hillside hideaway for the rich and famous, are multi-million dollar mansions with ocean views.
Unseasonably hot weather and dry conditions mean southern California is at particular risk from wildfires at present.
A year ago, a series of wildfires in the region destroyed some 2,000 properties and forced half a million people to flee their homes.
Bookmark with:
What are these?