Firefighters this afternoon gained the upper hand on a 20-acre brush fire near lake Piru, authorities said.

The majority of the flames were out and firefighters had cut line around 25 percent of the burned area by 3:30 p.m., said Bill Nash, a spokesman for the Ventura County Fire Department. Some flames were still burning this afternoon on the fire’s south flank.

“We’re out ahead of it,” Nash said. Fire department officials are confident the fire will be contained by nightfall.

No structures were threatened by the fire, and no injuries were reported.

No information was available today about what started the blaze, which was reported at 12:22 p.m. on East Holser Canyon Road about half way between Piru and Lake Piru.

Pushed toward Piru Canyon Road by 10 mile per hour winds, the fire grew to 20 acres by 2:20.

More than 100 firefighters and support staff from the Ventura County, Santa Paula and Santa Barbara County fire departments, the California Department of Forestry and Fire Service and the U.S. Forest Service rushed to the scene and stopped the blaze at 20 acres.

Water drops from helicopters and air tankers assisted with the firefighting effort.

“With the forecasts that we had for hot weather this weekend, we beefed up staffing levels, and when the fire broke out we were able to respond with a full attack on it,” Nash said.

The area where the fire is burning was also scorched by last year’s Ranch Fire. Fed by early winter rains, light grasses grew back in the burned area.

Those grasses burn quickly, but grass fires are easier to combat than blazes in heavier fuels, Nash said.

Today was predicted to be the hottest day of the first heat wave of the season.

Hot and dry conditions are expected to continue Saturday with temperatures as high as 104 in local valleys, the National Weather Service reported.

Temperatures around 100 are expected to continue in the hottest parts of the county Sunday before declining to the mid to lower 90s next week. Warm conditions with highs in the 70s are expected at beaches through next week.

No wind is predicted for the weekend.

Low humidities are expected, but not low enough to push fire danger to a critical level, Nash said.

“We have concerns, but what we’re not seeing right now are the conditions that have led to some of the firestorms we’ve experienced.”