Pushed by fierce Santa Ana winds, a 4,000-acre wildfire crept toward about 200 large, ridge-top homes Friday, prompting a voluntary evacuation.

A wall of flames as high as 30 feet snaked along hillsides in the morning and by the afternoon a huge plume of whiskey-brown smoke carried ash to the nearby Pacific Ocean.

The fire's estimated size doubled late Friday after firefighters had a chance to do a more accurate survey by helicopter, said Michele Faina, a department spokeswoman.

The late-season blaze was first reported around 3:30 a.m. in School Canyon — a hilly, rocky area between Ventura and Ojai, about 60 miles northwest of Los Angeles. Wind gusts of more than 50 mph helped the fire more than triple in size in just a few hours.

"We have a lot of crews up there and are making every effort to protect those structures," said Joe Luna, a spokesman for the Ventura County Fire Department. "It's right in their backyard."

Two nearby schools were closed and two Red Cross shelters opened to assist evacuees, though no one had gone to them as of early afternoon.

Besides homes, the hills also have a number of oil pumps. Although the cause of the fire was under investigation, it started in "the area of an oil field facility," according to Ventura County Fire spokeswoman Rose Rigalado.

About 1,000 firefighters and other personnel were at the scene, using bulldozers, water-dropping helicopters and fixed-wing aircraft in their effort to stop the blaze. One firefighter suffered minor injuries.

High winds posed problems for the crews. Shifting gusts reached 64 mph at nearby Laguna Peak.

"When the winds die down, it allows us to make better progress but we expect to deal with it throughout the day," Luna said.

Most of Southern California was under a red flag warning, which advises of warm, windy and dry conditions that could lead to explosive fire growth.

Fire officials said requirements that brush be cleared around homes were helping their efforts.