Firefighters and aircrews battled a 750-acre wildfire Wednesday in the rugged San Gabriel Mountains above the northeastern suburbs of Los Angeles, as high heat and extremely dry air arrived after weeks of unusually mild summer weather.

No homes had burned and no injuries were reported, but picnickers and campers fled and 18 Boy Scouts had to be flown out of the area after the blaze broke out. A voluntary evacuation was in effect for a tiny community in the area.

Much of the region awakened to the pungent smell of smoke from the so-called Morris Fire burning in Angeles National Forest six miles north of the foothill city of Azusa. Air quality regulators warned of unhealthy conditions, especially in the suburban valleys to the east.

Forecasters posted red flag warnings for fire danger across a broad swath of the region due to low humidity and hot temperatures, but the weather outlook did not call for any strong Santa Ana winds that typically stoke the worst Southern California wildfires.

The fire, which erupted Tuesday near Morris Dam in San Gabriel Canyon, was 10 percent contained as temperatures headed up to triple digits, said forest dispatcher Chris Rush.