Authorities reinstated a voluntary evacuation advisory Thursday in two mountain communities east of San Diego after winds fanned a wildfire that has burned nearly 54,000 acres.

Residents in parts of Warner Springs and Chihuahua Valley were told they should be prepared to flee with one hour's notice as wind pushed the fire back toward their homes. A day earlier, authorities decided to allow more than 1,200 people in the area to return home.

Crews have built a fire line around 60 percent of the blaze, which has destroyed 30 homes, 92 barns and other outbuildings, and 118 vehicles. It started July 29 after a National Guard helicopter on an anti-drug patrol clipped a power line in the area 70 miles northeast of San Diego.

Officials hope the fire will lose momentum as it approaches desert areas in the Anza-Borrego Desert State Park. Abby O'Leary, a spokeswoman for the California Department of Forestry, said at least 26 firefighters have suffered minor injuries in the fire and the cost of fighting it was estimated at more than $15 million.

Elsewhere, two huge wildfires merged in southwestern Oregon on Thursday but fire officials said they believed that 17,000 residents in the Illinois Valley were relatively safe.

The Florence Fire, at 296,000 acres, is the nation's biggest active fire. It was only 15 percent contained Thursday.

In central Nebraska, a wildfire firefighters thought they had contained flared up Wednesday amid gusting wind and quickly doubled in size to 20,000 acres, threatening several ranch homes.