Firefighters reported significant progress Wednesday against one of the biggest wildfires in California's history, but it was still spewing an enormous plume of smoke, dangerously contaminating the air across California and Nevada.
Authorities urged people in the region to avoid all outdoor activity as the Rim Fire's choking haze — a mile and a quarter thick at some points — spread from the outskirts of Yosemite National Park into Nevada. "Unhealthful" and "very unhealthy" air quality readings were recorded Wednesday across the Reno and Carson City area.
The fire had grown from 144,000 acres Sunday to about 192,500 acres by Wednesday evening, about the size of New York City. It had destroyed 111 structures and was threatening 5,500 more — 90 percent of them residences, the California Department of Forestry and Fire Protection said.
It's already the seventh-biggest fire in state history — and it's only 30 percent contained after almost two weeks of herculean effort by firefighting crews.
But Wednesday, officials said they were beginning to turn the tide, and they cautiously said they expect full containment my mid-September.
"It's looking better every day," Glen Stratton, a spokesman for the incident team, told NBC station KCRA of Sacramento. "So far, everything is holding."
Crews set a series of ground fires designed to choke off the blaze by burning up dry tinder ahead of it. If conditions allow, they're expected to begin a large burning operation inside Yosemite National Park from the Hetch Hetchy Reservoir — the only municipal water supply in a national park — southward, incident commanders said.
Many parts of the park remained closed as more than 4,500 firefighters labored to keep it safe.
The Rim Fire was among the fastest-moving of dozens of large wildfires raging across the parched West. The fires have strained resources and prompted fire managers to open talks with Pentagon commanders and Canadian officials about possible reinforcements.
Much of the terrain is steep and rocky, and if firefighters were dropped into the burn zone, there would be no escape route.
So firefighters are deploying a massive DC-10 jet to attack the fire from the air. Crew members can drop nearly 12,000 gallons of fire retardant from the plane's payload on each run. Each drop helps slow the flames as the retardant paints the hillsides red. At least 15 helicopters and other fixed-wing aircraft were also in use to battle the blaze from above.
On a helicopter flight 10,000 feet above the Rim Fire, NBC News reported flames leaping hundreds of feet into the air and fiery hot spots on the forested slopes of the Sierra Nevada as the blaze consumed broad areas.
Mandatory evacuations have been ordered in the Scotts Ridges area and an area south of California Highway 120 and north of Old Yosemite Road. Voluntary evacuations were advised around Tuolumne City and around the western boundary of Yosemite.
Elite Hotshot crews were stationed near residential areas, their first priority to protect life and property, and residents were confident in their ability to do that.
"I have incredible faith in the firefighters," Sarah Whitney of Tuolumne City told NBC Bay Area. "They're walking around in their tactical uniforms and dumping retardant. ... All that work, it's amazing."
Posters in towns and cities close to the fire thanked the crews for their work.
While this summer's massive fires may have fed a perception that wildfires are getting worse every year, the National Interagency Fire Center reported Wednesday that 2013 has recorded the fewest wildfires by Aug. 28 in the past 10 years and the second-smallest number of acres burned — about 3.6 million, half of last year's acreage.
Alastair Jamieson and Jeff Black of NBC News contributed to this report.