Massive California wildfire becomes 5th largest in state history

A seventh person died in a northern California wildfire on Saturday, as a couple of other fast-growing wildfires in the state expanded by more than 25 per cent overnight and continued to spread.

17 major fires burn as Trump declares disaster

An air tanker drops retardant on a fire near Clearlake Oaks, Calif., on Sunday. (Noah Berger/AFP/Getty Images)

A massive, out-of-control northern California wildfire that destroyed 68 homes and forced thousands to flee has become the fifth largest in state history, officials said on Sunday, as crews battled high temperatures and strong winds.

The Mendocino Complex Fire, made up of two separate conflagrations that merged near Ukiah, north of Sacramento, exploded by 25 per cent overnight and had blackened more than 1,000 square kilometres as of Sunday morning, the California Department of Forestry and Fire Protection said.

"The Mendocino Complex Fire has charred more than 254,000 acres [102,790 hectares], making it the fifth largest blaze in California's history," AccuWeather said on its website. "Firefighters will continue to face local gusty winds and building heat this week."

The Mendocino is one of 17 major wildfires burning across California that prompted U.S. President Donald Trump on Sunday to declare a "major disaster" in the state, ordering federal funding to be made available to help recovery efforts.

7th person dies in blaze

"Assistance can include grants for temporary housing and home repairs, low-cost loans to cover uninsured property loses and other programs to help individuals and business owners recover from the effects of the disaster," the White House said in a written statement.

The PG&E Corporation said on Sunday that a 21-year-old apprentice lineman, Jay Ayeta, had been killed when his vehicle crashed in western Shasta County as he worked with crews in dangerous terrain to battle the nearly two-week-old Carr Fire.

A residence is engulfed in flames from the Ranch Fire, one of two wildfires that make up the Mendocino Complex in California. (Noah Berger/AFP/Getty Images)

Ayeta was the seventh person to die in that blaze, which has scorched more than 62,000 hectares in the scenic Shasta-Trinity region north of Sacramento, including two young children and their great-grandmother whose home was overrun by flames, a resident who authorities said refused to leave his home despite evacuation orders, and two firefighters.

Firefighters had managed to contain 41 per cent of the Carr blaze by Sunday, and authorities were letting some evacuees return.

There are at least 16 large wildfires threatening 17,000 homes in California 0:35

This year, California wildfires have burned more land earlier in the fire season than usual, Cal Fire director Ken Pimlott said during a news conference on Saturday.

"Fire season is really just beginning. What seems like we should be in the peak of fire season, historically, is really now the kind of conditions we're seeing really at the beginning," he said.

Through last week, California fires had torched about 117,300 hectares, more than double the five-year average over that same period, according to Cal Fire.

A firefighter douses flames while battling the Ranch Fire near Clearlake Oaks, Calif., on Saturday. (Noah Berger/AFP/Getty Images)