SAN FRANCISCO — Thousands of people were under orders to evacuate broad areas of Northern California Wednesday as some 30 wildfires blazed across the state amid a blistering heat wave now in its second week.

"Throughout the state of California right now, we are stretched thin for crews" because of the fires, said Will Powers, a state fire spokesman. "Air resources have been stretched thin throughout the whole state." 

Thousands of homes and businesses were threatened in the wine-growing counties of Napa and Sonoma in an area devastated by a series of deadly blazes in the last three years. At least seven fires were grouped together as one of two major Lightning Fires in Northern California, a nod to their origins just a day earlier. 

Fire officials warned of "extreme fire behavior" challenging firefighters there, including strong winds. Powers said much of the fire was burning through rural areas with steep terrain, making it difficult to get crews in.

Police and firefighters went door-to-door in Vacaville early Wednesday in a frantic scramble to warn residents to evacuate, KPIX-TV reported. Footage showed some homes in flames. 

In Napa County, Gail Bickett, 80, loaded up her three dogs in a truck to evacuate as the fire burned behind houses across the road, the San Francisco Chronicle reported.

"It's scary," she said. "It's overwhelming."

Firefighters take refuge in their trucks in a cleared field as a wildfire also known as the Hennessey Fire jumped Knoxville Berryessa Road, west of Sacramento, Calif., Tuesday, Aug. 18, 2020. (Kent Porter/The Press Democrat via AP)

Blazes engulfed rural and forest areas near the San Francisco Bay Area, near Salinas in Monterey County, around Oroville Dam north of Sacramento, forested areas west of Silicon Valley, in remote Mendocino County and near the Nevada state line north of Lake Tahoe. 

Several also were burning in northern coastline areas and in Southern California.

Gov. Gavin Newsom ordered a statewide state of emergency Tuesday. 

The cluster of wine country fires threaten an area that only last year grappled with another massive blaze that forced 200,000 to flee — a task made more complicated this year because of the pandemic. 

Tuesday afternoon, the fire was moving toward an area called Atlas Peak that burned in 2017 in a blaze that killed six people and destroyed nearly 800 buildings. 

Robin Sisemore hosed down vegetation in front of her mother's adjacent house. Both homes were new, replacing ones that burned just three years ago. 

To the south, evacuations were ordered for all of Boulder Creek to the west of Silicon Valley, a community of 5,000 high in the Santa Cruz mountains where windy, long, forested roads, some paved, some dirt, can easily become blocked during storms or fires.