Flames raged unchecked for a second day through tinder-dry brush and scrub oak in Northern California's ranch country on Thursday after destroying three homes and forcing hundreds of residents to flee, as firefighters sought to benefit from subsiding winds, officials said.

The blaze, which has scorched some 8,300 acres (34 square km) of California's rural Lake County, was one of 14 large conflagrations under attack by nearly 7,000 firefighters statewide, forestry authorities said.

To help reinforce thinly stretched resources, the California National Guard mobilized nine of its helicopters Thursday morning to help battle the fiercest fires, state emergency management officials said.

The fires have been stoked by high winds, extremely low humidity and a heat wave that has brought triple-digit temperatures to much of the drought-parched state.

The so-called Rocky Fire erupted on Wednesday afternoon in the rugged foothills and canyons on the inland flanks of California's northern coastal range, 110 miles (180 km) north of San Francisco.

The blaze, propelled by strong winds, grew quickly during its first 12 hours, devouring three homes and numerous outbuildings, said Kaaren Stasko, a spokeswoman for the California Department of Forestry and Fire Protection.

About 500 people were ordered to evacuate, with emergency shelters opened for the evacuees and their livestock, she said.

Stasko said winds abated considerably on Thursday, though the 600-plus firefighters assigned to the blaze, backed by air tankers and water-dropping helicopters, had yet to achieve any measurable containment of the flames.

"Everything is very dry, and this fire has moved extremely fast," said Suzie Blankenship, another CalFire spokeswoman.

Smoke from the blaze was visible up to 80 miles (130 km) to the south in Napa, one of the state's famed wine-making regions, where a separate fire burning for the past week forced the evacuation of 200 people on Wednesday.

The Wragg Fire, near Lake Berryessa in Napa County, was 80 percent contained on Thursday after charring 7,500 acres (30.35 square km), fire officials said.

North of Sacramento, a 2,300-acre (9.3-square km) blaze had threatened 1,550 homes and other structures at its height, but 60 percent of that fire was contained by Thursday and evacuation orders were downgraded to advisories, officials said.

In the Southern California county of San Bernardino, east of Los Angeles, officials posted a $75,000 reward on Tuesday for information leading to the arrest and conviction of drone hobbyists whose aircraft have interfered with recent firefighting efforts there.