The Highland Fire in rural Riverside County southeast of Los Angeles was only mildly active as Santa Ana winds that pushed it through brushy hills eased and fire crews had it 20 per cent contained by Wednesday night, said Rob Roseen, a fire spokesperson

"It was favourable conditions for firefighters" but humidity remained low and rugged terrain made the work challenging for the approximately 1,200 firefighters, Roseen said.

The size of the blaze remained unchanged at just under 4 square miles (10 square kilometers)

Gusty, dry Santa Ana winds were blowing Monday when the fire erupted near rural Aguanga in Riverside County about 53 miles (85 kilometers) north of San Diego. Evacuation orders were issued for 4,000 residents as flames spread rapidly

With progress being made against the blaze, many evacuation orders were reduced to warnings on Wednesday, and several thousand people were allowed to return home but about 2,500 homes and other buildings remained threatened, authorities said

Although the forecast for the next few days was favourable, those allowed back home should remain vigilant, Roseen said

The Santa Ana winds, which have a long history of stoking the region's wildfires, blow out of the interior toward the Pacific Coast. The dry air saps moisture from vegetation, making it easier to burn. Forecasters predicted a return of moist ocean air by Friday