A wildfire raging through coastal mountains in California is threatening ranches and rural homes as the fire-scarred US state faces a new round of dry winds that raise the risk of infernos.

The Alisal Fire covers more than 24 square miles in the Santa Ynez Mountains west of Santa Barbara, and the number of firefighters tackling the blaze has nearly doubled to 1,300, with more on the way.

While the scenic region along the Pacific shoreline is lightly populated, the blaze was a threat to more than 100 homes, ranches and other buildings, fire officials said.

Fire crews were protecting Rancho del Cielo, which was once owned by Ronald and Nancy Reagan and was known as the Western White House during his presidency.

Crews works to extinguish a fire in California
Crews works to extinguish a fire in California (Mike Eliason/Santa Barbara County Fire Department via AP)

The 688-acre ranch where Mr Reagan hosted world leaders sits on top of the mountain range, above the flames feeding on dense grasses.

Based on staff reports from the ranch, the fire was about a half a mile away, but that section of the blaze was not as active as others, said Jessica Jensen, vice president and chief of staff of the Young America’s Foundation, which now operates the ranch.

“We are thankful that there has been no fire activity on the actual Reagan ranch property. The ranch, itself, is still in a very defensible position,” Ms Jensen said.

The area has not burned since 1955, according to the youth organisation.

Fire engines were on the ranch property, and fire retardant will be sprayed around its structures, the foundation said in a statement. It noted that helicopters have filled up with water from one of the ranch’s two lakes.

A wildfire burns near a home in Goleta, California
A wildfire burns near a home in Goleta, California (Ringo HW Chiu/AP)

Crews also protected an Exxon/Mobil facility in a canyon surrounded by flames.

The fire erupted on Monday near the Alisal Reservoir, and powerful winds from the north swept the flames down through the mountains. At one point, the fire jumped a four-lane motorway and reached a beach.

Firefighters working in steep, rugged terrain got help from more than a dozen water-dropping air tankers and helicopters that returned to the skies amid calmer daytime winds.

The National Weather Service said there would be a new round of south Santa Barbara County’s notorious Sundowner winds, and other parts of California were also expected to experience increased fire danger.

California wildfires have scorched nearly 3,900 square miles this year and destroyed more than 3,600 homes, businesses and other structures, according to the state Department of Forestry and Fire Protection.