‘There is nothing left’: After a town is wiped out, more of California is threatened.

After the Dixie Fire destroyed the Gold Rush town of Greenville, Calif., local officials said they were hopeful that improving weather conditions on Friday would help firefighters prevent the blaze from dealing further damage.

At a community meeting on Thursday night, a meteorologist told residents of threatened towns several hours north of Sacramento that winds were expected to decrease and that the wildfire smoke would keep temperatures on the ground cooler. He said there was no sign of the strong weather systems that had plagued this week.

Still, the fire continued to expand at an alarming pace. Overnight, it grew to nearly 433,000 acres, according to The New York Times wildfire tracker, becoming the third-largest blaze in recorded California history — up from sixth the day before — and the largest wildfire now burning in the United States, surpassing the Bootleg Fire in southern Oregon.

Nobody was resting easy after seeing the destruction that shifting winds had brought to Greenville, a town of about 1,000 people.

“It looks like a bomb went off,” said Ryan Meacher, 37, whose father’s house in Greenville was one of many that burned down. “There is nothing left.”

Mr. Meacher lives in Grass Valley, which is itself being threatened by the River Fire, and said it was heartbreaking to think about what was lost in Greenville — the library where he would pick up books and VHS tapes, the pizza place next door with an arcade.

Also destroyed was a charter school where Kjessie Essue’s husband works and the Cy Hall Memorial Museum, which covered the history of Indian Valley and which her parents spent hundreds of hours building.

Ms. Essue, 38, lives in nearby Taylorsville and evacuated south on Thursday with her Nigerian Dwarf goats, her husband, her three young children and her parents, who do not know whether their Greenville home still stands.

She said it seemed liked a movie as they packed up, with an alarm blaring and wild winds sending a smoke plume with a black center toward the area.

“Greenville is a wasteland,” she said. “It’s surreal.”

Sheriff Todd Johns of Plumas County said at the community meeting that there were no reported injuries but that the authorities were still looking for four people who were unaccounted for. He estimated that the blaze had destroyed more than 100 homes in the area.

“My heart is crushed by what has occurred there, and to the folks who have lost residences and businesses,” said Sheriff Johns, a lifelong Greenville resident.

The Dixie Fire is 35 percent contained and has burned across parts of four counties. Officials said that the blaze seemed to have spared Chester, burning around both sides of the town off Lake Almanor, but that other communities — Westwood, Crescent Mills — closer to Greenville remained under threat.

On Sunday, the authorities had lifted a mandatory evacuation order for Greenville after several days of favorable weather. But then the wind changed directions three times in two days, explosively spreading the Dixie Fire.

“We’re seeing truly frightening fire behavior, and I don’t know how to overstate that,” said Chris Carlton, supervisor for the Plumas National Forest. “We have a lot of veteran firefighters who have served for 20, 30 years and have never seen behavior like this.”

Gov. Gavin Newsom declared a state of emergency for three counties on Thursday, noting that “strong winds, high temperatures, drought conditions, and dry fuels have further increased the spread” of the Antelope Fire in Siskiyou County, on the Oregon border, and the River Fire in Nevada and Placer Counties, northeast of Sacramento.

The River Fire, which has grown to 2,600 acres since starting on Wednesday, has destroyed 76 structures and injured three people, including a firefighter. It is 15 percent contained but threatens 3,400 more structures, with 24,000 people living within five miles of the blaze, according to the New York Times fire tracker.