UPDATE 4-Residents flee wildfire raging through Southern California canyon

(Updates numbers of acres burned, people evacuated)

By Dan Whitcomb

LOS ANGELES, Dec 3 (Reuters) - Two firefighters were injured and residents of a rustic Southern California canyon were driven from their homes after a blaze broke out overnight at a house and tore across more than 7,000 acres of dry brush and wooded hillsides.

Some 500 firefighters aided by water-dropping aircraft were battling the flames, which sent smoke drifting across Orange and Los Angeles counties and out over the Pacific Ocean. Some 25,000 people were evacuated across Orange County.

The Bond Fire, named for the street where it started, ignited around 10 p.m. Wednesday night and was quickly whipped through Silverado Canyon by gusty Santa Ana winds.

"I got a text message from my neighbor saying, 'Are you okay? Your street is on fire,'" said Giovanna Gibson, 60, who lives on Bond Street. She was at her small business office near John Wayne Airport at the time.

Gibson said she wouldn't have received that warning had she been home in Silverado Canyon, which has little cell phone reception.

Neighbors told Gibson the blaze ignited when the owners of a home without power tried to start their generator and it exploded. Fire officials have not yet said what they believe to be the cause of the fire.

Southern California Edison had cut power to parts of the canyon at the outset of the hot, dry Santa Ana winds, and Gibson said that may have hampered efforts by authorities to send evacuation warnings.

An Edison spokesman confirmed that the utility had cut power to some of the homes in the canyon.

Woodsy Silverado Canyon, miles from Southern California's suburban sprawl up a single winding road, is home to an eclectic mix of residents including artists, horse owners and ranchers.

The blaze had blackened more than 7,000 acres by the time darkness fell on Thursday and was zero percent contained.

Two firefighters were injured and were transported to a local hospital for further treatment, the Orange County Fire Authority said on Twitter.

Fire managers said they believed a number of homes and other structures had been damaged or destroyed by the blaze but could not yet provide details.

"We're in December and we now have active wildfires still in our state," California Governor Gavin Newsom said at a press briefing. "These Santa Ana winds have been quite intense."

Since the start of the year, wildfires have scorched more than 6,500 square miles (17,000 square km) of California land, according to the California Department of Forestry and Fire Protection.

The yearly land area burned in the western United States has grown eight times larger in less than four decades, the U.S. Forest Service Rocky Mountain Research Station said in research published last month. (Reporting by Dan Whitcomb in Los Angeles; Additional reporting by Jonathan Allen in New York; Editing by Bill Tarrant and Leslie Adler)