In pictures: Northern California wildfires threatening thousands of homes

A car burns while parked at a residence in Vacaville, California during the LNU Lightning Complex fire. As of the late hours of August 19 the Hennessey fire has merged with at least 7 fires and is now called the LNU Lightning Complex fires. Dozens of fires are burning out of control throughout Northern California as fire resources are spread thin.

In central California, a pilot on a water dropping mission in western Fresno County died Wednesday morning when his helicopter crashed about an hour from New Coalinga Municipal Airport. Above, an air tanker drops retardant as the LNU Lightning Complex fires tear through the Spanish Flat community in unincorporated Napa County, Calif. Fire crews across the region scrambled to contain dozens of wildfires sparked by lightning strikes as a statewide heat wave continues.

The fires, many caused by lightning and sometimes pushed by strong winds, had burned hundreds of thousands of acres as they chewed through brushland, rural areas, canyon country and dense forest to the north, east and south of San Francisco. Fires also carved their way through the wine country and the Sierra Nevada.Above, flames from the LNU Lightning Complex fires jump Interstate 80 in Vacaville, Calif.The highway was closed in both directions shortly afterward.

Residents in nearby Vacaville, a city of about 100,000 located between San Francisco and Sacramento, were roused before dawn by orders to flee.Police and firefighters went door-to-door in a frantic scramble to warn residents to evacuate as flames encroached.

Burned vehicles rest beneath a tree after the complex fires tore through Vacaville, Calif. Ash and smoke filled the air in San Francisco from at least seven fires _ known as the LNU Lightning Complex _ that had burned more than 100 buildings, including some homes, and threatened 25,000 others in Napa, Sonoma, Lake, Yolo and Solano counties.

An alpaca sits next to a burned out truck after the fire moved through the area in Fairfield, California.

Local residents work frantically to save a friend's home from an approaching wildfire in Vacaville, Calif. Thousands of people were forced to flee their homes in Vacaville, a city of about 100,000 residents near Sacramento, as a combination of uncontrolled fires continued to threaten Northern California on Wednesday.

Firefighters monitor flames as they approach a residence in the valley area of Vacaville, northern California.

Wildfires raged through Northern California, threatening thousands of homes and blackening the skies near San Francisco as crews struggled to surround them despite steep terrain and blistering heat.

The San Francisco skyline stands in San Francisco, California.Smoke from multiple wildfires in Northern California has polluted the air, sparking concern for residents with respiratory issues especially those suffering from Covid-19. Atmospheric testing revealed Northern California’s air quality to be the worst in the world, according to the San Francisco Chronicle.

Smoke rises from the LNU Lightning Complex wildfires as seen from an AlertWildfire camera looking east from Mount St. Helena, north of Calistoga, California.

Pacific Gas and Electric firefighters extinguish spot fires as the LNU Lightning Complex fire burns through the area in Fairfield, California. Hundreds of fires have erupted since the start of the week as a heat wave accompanied by humid air created a dangerous mix of triple-digit temperatures and thunderstorms that flashed lightning.

Flames are seen along the east side of Lake Berryessa near Berryessa Highlands, California.