Stephen Lam/Getty Images

Wildfires expanded their deadly reach in northern California on Sunday, threatening thousands of people and burning hundreds of structures to the ground.

The so-called Valley Fire quickly spread across 40,000 acres on Saturday night, forcing residents of Lake and Napa counties to flee as their homes went up in flames.

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The town of Middletown was particularly hard hit:

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By Sunday afternoon, the fire was still raging and showed no signs of stopping.

California's government ordered mandatory evacuations in several parts of the area and declared a state of emergency.

This wildfire season has been particularly fierce, thanks in part to an unprecedented drought. California's emergency services chief said that the fires plaguing the state were the worst he's seen in 30 years.

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“The bushes, the trees have absolutely no moisture in them, and the humidities are so low that we are seeing these ‘fire starts’ just erupt into conflagrations,” Mark Ghilarducci told the Sacramento Bee.

MIDDLETOWN, CA - SEPTEMBER 13: A firefighter with the CalFire Santa Clara Unit carries a flare to set backfire along Highway 29 during the Valley Fire on September 13, 2015 in Middletown, California. The fast-moving fire has consumed 40,000 acres and is currently zero percent contained. (Photo by Stephen Lam/ Getty Images)
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MIDDLETOWN, CA - SEPTEMBER 13: Smoke rises from charred vegetation in a distance during the Valley Fire on September 13, 2015 in Middletown, California. The fast-moving fire has consumed 40,000 acres and is currently zero percent contained. (Photo by Stephen Lam/ Getty Images)
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MIDDLETOWN, CA - SEPTEMBER 13: A playground slide stands undamaged among smoldering rubble during the Valley Fire on September 13, 2015 in Middletown, California. The fast-moving fire has consumed 40,000 acres and is currently zero percent contained. (Photo by Stephen Lam/ Getty Images)
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MIDDLETOWN, CA - SEPTEMBER 13: A car burns in front of a burning home during Valley Fire on September 13, 2015 in Middletown, California. The fast-moving fire has consumed 40,000 acres and is currently zero percent contained. (Photo by Stephen Lam/ Getty Images)
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Note: this story was updated on Sunday afternoon to include the latest news about the fire.