California Governor Jerry Brown declared a state of emergency as raging wildfires spread in the northern part of the drought-ridden US state, forcing thousands to flee the flames.

The monster blazes have charred more than 100,000 acres (40,470 hectares), authorities said, destroying hundreds of homes and commercial structures and mobilizing thousands of firefighters.

Eight major fires are currently burning but two -- one about 100 miles (160 kilometers) southwest of the state capital of Sacramento and the other about 100 miles to the east -- have been particularly damaging over the last week, with little letup in sight.  

Driven by dry conditions, high winds and soaring temperatures, the Butte Fire has burned 65,300 acres and was just 25 percent contained while the Valley Fire had grown to 50,000 acres and was zero percent contained, state fire agency CAL FIRE said late Sunday.

Governor Brown issued "an emergency proclamation for Lake and Napa counties due to the effects of the Valley Fire, which has burned thousands of acres of land and caused the evacuation of residents and damage to highways and other infrastructure," his office said.

The town of Middletown, population 1,300, was particularly devastated by the Valley Fire, according to local daily Santa Rosa Press-Democrat, which said the fire grew from 50 acres to 10,000 over just five hours Saturday -- before quadrupling in size overnight.

"I'm looking in all directions, and all I see