RANCHO CUCAMONGA, Calif. (AP) -- A fresh blast of strong winds hit a wildfire on Thursday in the foothills east of Los Angeles but did not spread the blaze that drove people from 1,600 homes, officials said.
The fire remained within the previous burn area despite new winds that reached 60 mph, the U.S. Forest Service said.
The winds still brought trouble, however, forcing the grounding of helicopters and planes that were being used to fight the fire that began Wednesday in San Bernardino National Forest.
The lack of aircraft also prevented an accurate mapping of the blaze that has charred at least 1,000 acres and likely many more, the Forest Service said.
The fire was 10 percent contained after an initial surge on Wednesday that included a gust of winds that topped 100 mph.
Nine schools in nearby Rancho Cucamonga were closed for a second day on Thursday due to the fire danger, and residents who had been allowed to return home after evacuations were warned to be ready to leave again.
"The message is, 'ready, set, go,'" said Rancho Cucamonga Fire Chief Mike Bell. "Be ready just in case something changes."
Some 700 firefighters with 55 fire engines and four bulldozers were building containment lines around the west edge of the blaze, nearest homes.
The National Weather Service issued a red-flag warning of extremely dangerous fire conditions for Los Angeles, Orange and Ventura counties until 8 p.m. Thursday.
The fire erupted in the midst of a heat wave that has sent temperatures into the 90s in some areas.
High temperatures were expected to continue through Saturday, with humidity in the single digits.