Southern California's largest wildfire, a devastating blaze that has already destroyed hundreds of homes in Ventura County, continued to grow Sunday and was threatening seaside communities in Santa Barbara County and prompting new evacuation orders.

Officials say the largest, most destructive wildfire burning in Southern California is expected to grow as it enters its second week.

The Thomas Fire north of Los Angeles has burned more than 270 square miles, prompted tens of thousands of evacuations and destroyed nearly 800 structures.

The National Weather Service says gusts up to 40 mph are expected through Monday.

The 230,000-acre Thomas fire, now in its seventh day, is threatening an estimated 18,000 structures, according to Cal Fire.

"Over the last 12 to 14 hours, we've experienced some extreme fire behavior on the fire," Mark Brown, operations section chief of Cal Fire told reporters at a Sunday evening briefing.

He said the fast-moving blaze had moved some 7 miles to the west in a 12 to 14-hour period, burning about 56,000 acres in the process. As a result, officials revised containment downward, from 15 percent to only 10 percent.

Officials ordered mandatory evacuations for at least 1,000 residents in southern Santa Barbara County, including portions of Carpinteria. Also, evacuation warnings were issued for parts of Montecito and Summerland, two communities known for multimillion-dollar homes and celebrity estates.

Oprah Winfrey and actor Rob Lowe are among the famous with homes in the Montecito area. They both tweeted Sunday about the fire approaching the town and offering prayers.

https://twitter.com/Oprah/status/940058257141391362

Lowe tweeted Sunday morning that he was "packing to evacuate now."

https://twitter.com/RobLowe/status/939896964807770112

Also, TMZ reported that Ellen DeGeneres' new home was under threat. She purchased a home in Carpinteria back in October.

https://twitter.com/TheEllenShow/status/939945041467867136

As of Sunday, fire officials estimated the cost to date of fighting the Thomas fire at approximately $34 million.

California Gov. Jerry Brown visited fire areas Saturday and told reporters, "We're facing a new reality in the state where fires threaten people's lives, their property, their neighborhood, and of course billions and billions of dollars. So we have to have the resources to combat the fires."