A Southern California wildfire has destroyed 132 structures, mostly homes, in less than two days, fire officials said as raging winds were forecast to ease.

The fire started on Wednesday morning in Ventura County and has grown to about 32 square miles (83 square kilometres) at 5% containment. Its cause has not been determined.

Ten people have been injured in the course of the fire, Ventura County Sheriff James Fryhoff said. Most of them suffered from smoke inhalation or other non-life-threatening injuries.

Fire officials said 88 other structures were damaged but did not specify whether they had been burned or affected by water or smoke damage.

California Winds Wildfires
Horses gallop in an enclosure at Swanhill Farms as the Mountain Fire burns in Moorpark, California (Noah Berger/AP)

Some 10,000 people remained under evacuation orders on Thursday as the Mountain Fire continued to threaten some 3,500 structures in suburban neighbourhoods, ranches and agricultural areas around Camarillo in Ventura County.

County fire officials said crews working in steep terrain with support from water-dropping helicopters were focusing on protecting homes on hillsides along the fire’s northeast edge near the city of Santa Paula, home to more than 30,000 people.

Officials in several Southern California counties urged residents to be on watch for fast-spreading blazes, power outages and downed trees during the latest round of notorious Santa Ana winds.

Santa Anas are dry, warm and gusty northeast winds that blow from the interior of Southern California toward the coast and offshore, moving in the opposite direction of the normal onshore flow that carries moist air from the Pacific.

They typically occur during the fall months and continue through winter and into early spring.

Ariel Cohen, the National Weather Service’s meteorologist in charge in Oxnard, said Santa Ana winds were subsiding in the lower elevations but remained gusty across the higher elevations on Thursday evening.

APTOPIX California Winds Wildfires
Jaime Hernandez sprays water to defend his home while battling approaching flames from the Mountain Fire (Stephen Lam/San Francisco Chronicle via AP)

The red flag warnings, indicating conditions for high fire danger, expired in the area except for in the Santa Susana Mountains, Mr Cohen said. The warnings will expire by 11am on Friday in the mountains.

The Santa Ana winds are expected to return early-to-midweek next week, Mr Cohen added.

The Mountain Fire was burning in a region that has seen some of California’s most destructive fires over the years. The fire swiftly grew from less than half a square mile (about 1.2 square kilometres) to more than 16 square miles (41 square kilometres) in little more than five hours on Wednesday.

By Thursday evening it was mapped at about 32 square miles (83 square kilometres) and Governor Gavin Newsom had proclaimed a state of emergency in the county.

The Ventura County Office of Education announced that more than a dozen school districts and campuses in the county were closed on Thursday, and a few were expected to be closed on Friday.

Utilities in California began powering down equipment during high winds and extreme fire danger after a series of massive and deadly wildfires in recent years were sparked by electrical lines and other infrastructure.

Power was shut off to nearly 70,000 customers in five counties over the heightened risk, Southern California Edison said on Thursday.