This home in the hills above Santa Barbara goes up in flames as a wind-whipped brush fire roared through the area on Wednesday. (Mike Meadows/Associated Press)

Dozens of homes in the hills above Santa Barbara have been destroyed by an out-of-control wildfire, California Gov. Arnold Schwarzenegger said Thursday.

More than 13,500 people have been forced from their homes as sweltering temperatures and high winds continue to fan the flames. Hundreds more homes remain under threat as the winds are expected to gust through the night.

Earlier in the day, Schwarzenegger declared a state of emergency as the rapidly moving blaze burned more than 500 hectares of land.

"We really can't do any containment lines. It's too dangerous," Santa Barbara County fire Capt. David Sadecki said. "We're doing some structure protection, but firefighters can be in a safe location one minute and in a dangerous situation the next."

Ten firefighters were hurt battling the blaze, at least two of them seriously, Sadecki said.

About 1,400 firefighters were on the lines, including crews from Monterey County and San Diego County, along with prison inmates from the California Department of Corrections. Eight helicopters dropped water through the night and eight fixed-wing aircraft were set to join them after dawn, officials said.

Santa Barbara County Sheriff's Department spokesman Drew Sugars said 5,430 homes were under mandatory evacuation. He estimated they were home to 13,575 people. Around 13,000 others were told to be prepared to evacuate.

Some evacuees were allowed to return home early Thursday, the county said in a news release, but officials had no estimate of how many people were affected.

Sudden spread

The fire, which began Tuesday, appeared to be dying down through most of Wednesday, said the CBC's Steve Futterman, reporting from Santa Barbara. But later that evening, gusts approaching 100 km/h hit the area, pushing the flames from north to south and into neighbourhoods around the town.

"There was really nothing firefighters could do. They tried to protect as many homes as they could and they were quite successful, but obviously many homes were destroyed," Futterman said. It's not immediately clear exactly how many buildings were destroyed in the blaze, he said, but initial reports indicated at least two dozen were affected.

"The suddenness of all this was just amazing. The fire overwhelmed both firefighters and homeowners, and some people barely escaped," Futterman said.

Aerial footage showed huge mansions and humble homes reduced to rubble, leaving palm trees swaying over gutted ruins. Three Ventura County firefighters were injured when flames overtook their fire engine as they tried to protect a building, their department said in a statement.

The BBC reported the blaze is being investigated as possible arson.

Santa Barbara, a city of 90,000, is located 160 kilometres northwest of Los Angeles. It dates to the Spanish colonial era and is a major tourist destination on the state's central coast.

The blaze is the second major fire to hit the area in less than six months. Another wildfire ravaged Santa Barbara County in November, claiming 210 homes and injuring more than two dozen people. Investigators concluded that fire was caused by a bonfire built by several young adults.

With files from The Associated Press