San Francisco, Jul 31 (IANS): The toll in the 17 wildfires that were currently blazing in California has increased to eight, according to authorities.

The Carr fire - in Shasta County, some 400 km north of San Francisco - began a week ago near the town of Redding and has been the most deadly of the blazes with six fatalities, including a 70-year-old woman and two of her grandchildren.

That fire has forced authorities to evacuate more than 38,000 people and has destroyed 723 residential structures but is only 20 per cent contained at present, California's forestry and forest fire prevention department, CalFire, told Efe news.

CalFire also said that seven people are missing in the Carr fire.

CalFire spokesman Chris Anthony said the fires are "explosive" and the situation is beyond "extreme".

Two other people were found dead near the Ferguson fire, which is 30 per cent contained, one of them a firefighter who died after being hit by a falling tree in Mariposa County, where his contingent of firefighters were working to quell the blaze.

The US National Weather Service said that excessive heat combined with low relative humidity and dry vegetation were setting up ideal conditions for the numerous fires.

Currently, there are 17 active - albeit isolated - wildfires in California, ranging from blazes in the southern part of the state all the way to the northern border with Oregon.

Some 12,000 firefighters are battling the flames around California, along with 800 members of the California National Guard, backed up by hundreds of fire trucks, some of which have come from as far away as Florida.

Mendocino County is the site of two other uncontrolled fires that have burned more than 12,000 hectares (30,000 acres) and forced hundreds of residents to evacuate.

California Governor Jerry Brown has declared a state of emergency for Riverside, Shasta and Mariposa Counties and on July 28, President Donald Trump signed an emergency declaration for the state, thus enabling the federal government to provide additional aid.