What is considered as the most destructive wildfire to hit California this summer has already claimed a fatality, injured four others and destroyed at least 400 homes and hundreds of other buildings as it continues to spread to thousands of acres of land.

The so-called Valley Fire, which erupted Saturday afternoon, has already torched 50,000 acres of land with containment at zero, according to the Los Angeles Times.

Sheriff Brian Martin said the fire is "the worst tragedy Lake County has ever seen." Fire officials called the rate of spread unprecedented.

By Monday morning the fire had torched about 61,000 acres of tinder-dry forests, brush and grasslands, and was only about 5 percent contained, according to the California Department of Forestry and Fire Protection (Cal Fire).

A total of 1,448 fire personnel and 157 fire engines have been deployed.

Gov. Jerry Brown declared a state of emergency Sunday for Lake and Napa counties to allow the state to use resources including the California National Guard.

He previously declared a state of emergency in Amador and Calavares counties in the Butte fire that destroyed 65,300 acres of land with 25 percent containment.

The fire department said 135 residences, 79 outbuildings and four structures were damaged in the fire, and threatening 6,400 more.

"It's very unsafe right now," said Cal Fire spokesman Scott McLean.

The fire spread quickly due to dried brush and trees due to last week's blistering heat. Winds fanned the fire that started from a small grass blaze to an inferno, the Los Angeles Times said.

The cause of the fire is still under investigation, according to Todd Derum, incident chief with Cal Fire, saying, "It was reported as a structure fire but it was outside of the structure."

During the fire, fire hydrants went dry. Residents who sneaked past the barricades declared that half of the town was destroyed.

"We tried the best we could, but it went structure to structure to structure," Derum said.

Two evacuation centres in Napa County Fairgrounds and at a high school in Kelseyville were filling up fast with evacuees and donations.