A three-week-old wildfire has destroyed historic buildings in a small town in northern California.

The Dixie Fire, swollen by bone-dry vegetation and 40mph gusts, raged through the Sierra Nevada community of Greenville on Wednesday evening.

A petrol station, hotel and bar were among many buildings gutted in the town, which dates to California’s Gold Rush era and has some structures more than a century old.

Buildings burn as the Dixie Fire tears through Greenville (Noah Berger/AP)

Plumas County Supervisor Kevin Goss said that the fire “burnt down our entire downtown. Our historical buildings, families’ homes, small businesses, and our children’s schools are completely lost”.

Officials could not immediately say how many buildings were razed, but photos and video from the scene indicated the destruction was widespread.

“We lost Greenville tonight,” politician Doug LaMalfa, who represents the area, said in an emotional Facebook video. “There’s just no words.”

A burnt-out car
Following the Dixie Fire, a scorched vehicle rests in a driveway in the Indian Falls community of Plumas County (AP)

As the fire’s north and eastern sides exploded on Wednesday, the Plumas County Sheriff’s Office issued a warning online to the town’s approximately 800 residents: “You are in imminent danger and you MUST leave now!”

The growing blaze that broke out on July 21 was the state’s largest current wildfire and has blackened over 504 square miles.

“We did everything we could,” fire spokesman Mitch Matlow said. “Sometimes it’s just not enough.”

The Dixie fire
The Dixie fire has been fuelled by stronger winds (AP)

About 100 miles to the south, officials said between 35 and 40 homes and other structures burned in the fast-moving River Fire that broke out on Wednesday near Colfax, a town of about 2,000 residents.

Within hours it ripped through nearly 4 square miles of dry brush and trees. There was no containment and about 6,000 people were under evacuation orders across Placer and Nevada counties, according to the California Department of Forestry and Fire Protection.

Earlier in the week, some 5,000 firefighters had made progress on the Dixie Fire, saving some threatened homes, bulldozing pockets of unburned vegetation and managing to surround a third of the perimeter.

More fire engines and bulldozers were being ordered to bolster the fight, Mr Matlow said.

On Wednesday, the fire grew by thousands of acres and an additional 4,000 people were ordered to evacuate, bringing nearly 26,500 people in several counties under evacuation orders, he said.

Red flag weather conditions of high heat, low humidity and gusty afternoon and evening winds erupted on Wednesday and were expected to be a continued threat.

Winds were expected to change direction multiple times on Thursday, putting pressure on firefighters at sections of the fire that have not seen activity in several days, officials said.

The trees, grass and brush were so dry that “if an ember lands, you’re virtually guaranteed to start a new fire”, Mr Matlow said.

The Dixie Fire was running parallel to a canyon area that served as a chimney, making it so hot that it created enormous pyrocumulus columns of smoke.

These clouds bring chaotic winds, making a fire “critically erratic” so it is hard to predict the direction of growth, he added.