A wind-driven brush fire that started late Monday afternoon in Los Padres National Forest near Highway 154 in Santa Barbara County moved quickly downhill, prompting mandatory evacuations and threatening homes.

The Cave fire started just after 4 p.m. near East Camino Cielo and Painted Cave Road and by 8 p.m. had grown to at least 2,500 acres, according to the Santa Barbara County Fire Department.

It initially moved into a few canyons and rapidly expanded as it was pushed south by 15-mph down-canyon winds with 30-mph gusts. By 7:30 p.m., the fire was spotting in front of itself and had started at least one spot fire near Highway 154 and Cathedral Oaks Road, said Mike Eliason, a public information officer with the department.

“As this fire gets pushed down canyon, it’s going to start getting closer to homes,” Eliason said.

The fire has burned down to the top of Cieneguitas Road near the San Marcos Foothills Preserve, according to Santa Barbara city’s Office of Emergency Services.

There is no information available on whether any homes have burned, said Capt. Daniel Bertucelli, a Santa Barbara County Fire Department public information officer.

“We’re going to fight fire throughout the night, and tomorrow when the sun comes up, we’ll get a better understanding of what sort of damage we have,” Bertucelli said.

Winds were expected to increase, especially at higher elevations, until about 1 a.m., with some areas of the Santa Ynez Mountains expected to see gusts of up to 65 mph, according to the weather service.

Bertucelli said that as he was driving 55 mph down Highway 154 earlier in the evening, the fire was keeping up with him, growing alongside the roadway. Once he reached lower elevations, though, the wind was much lighter.

Meteorologists were forecasting a decrease in wind through the early morning hours Tuesday, and the area was expected to see rain Tuesday afternoon or evening.

“Hopefully Mother Nature will help us out tomorrow,” Bertucelli said.

The fire is burning through dense, old brush, and that much of the area hasn’t burned since the Painted Cave fire in 1990.

The area where the Cave fire is burning was also dry, with relative humidity reported at 14% as of 5:25 p.m., according to the National Weather Service.

Mandatory evacuations have been ordered for the area of Highway 154 east to Ontare Road and from Foothill Road to the top of Camino Cielo. An evacuation warning has been issued for Highway 154 west to Fairview Avenue and Ontare Road east to Gibraltar Road.

As the fire grew, mutual aid started to arrive to help county and national forest firefighters. The Ventura County Fire Department sent two strike teams, about 10 fire engines, Monday evening, and the L.A. County Fire Department sent a Firehawk helicopter, which is capable of performing nighttime water drops.

This is a breaking news story and will be updated.