A 70-year-old woman and her two great-grandchildren were among six people killed when a wildfire engulfed entire communities in northern California, officials and family members said.

Shasta County Sheriff Tom Bosenko told a news conference near the city of Redding at the edge of the blaze on Sunday one more person had been killed in a residence consumed by fire, bringing the total to six, including two firefighters. He said the latest victim had not complied with an evacuation order.

Authorities are still looking for seven people after finding nine others who had been reported missing, Bosenko said.

More than 38,000 people remained under evacuation orders on Sunday in and around Redding, a city of 90,000 people about 160 miles (260 km) north of the state capital, Sacramento.

Redding Police Sergeant Todd Cogle confirmed that three bodies discovered at a fire-ravaged home on the outskirts of Redding were two children and their great-grandmother.

The victims were identified by relatives on their Facebook accounts and in news reports as James Roberts, 5, his sister Emily, 4, and their great grandmother, Melody Bledsoe, 70.

Bledsoe's granddaughter, Amanda Woodley, said on Facebook the elderly woman desperately put a wet blanket over the children as their home burned.

"Grandma did everything she could to save them," Woodley said.

The children's mother, Sherry Bledsoe, was quoted by the Sacramento Bee as saying: "My kids are deceased. That's all I can say."

Bledsoe's husband wept as he recalled trying to get back to the house after running an errand on Thursday, only to learn the fire was closing in on them. Ed Bledsoe told the Sacramento Bee he spoke to the children on the phone as he raced in vain to return in time to save them.

A Go Fund Me effort to help had raised half its $30,000 goal by Sunday.

The Carr Fire, which has destroyed more than 650 homes, is the deadliest and most destructive of nearly 90 wildfires burning from Texas to Oregon. The blazes have killed four firefighters in California in a little more than two weeks after officials reported on Sunday the death of a firefighter battling a wildfire by Yosemite National Park.

UNPREDICTABLE

The Carr Fire alone has charred 95,368 acres (38,594 hectares) of drought-parched vegetation since erupting last Monday - an area the size of Detroit.

It started last week as the result of a vehicle mechanical failure, authorities said.

The blaze remained unpredictable, said Chris Anthony, a division chief with the California Department of Forestry and Fire Protection (Cal Fire).

"Under these conditions that we are seeing right now, it's not going to take much for the fire to have the extreme spread that we saw a couple of days ago," he said. "We are simply not getting a break."

Officials said they were feeling more optimistic on Sunday afternoon and starting to gain ground on the Carr Fire. They pledged to return people to their homes as soon as possible.

Some 3,500 firefighters and a squadron of 17 water-dropping helicopters had carved buffer lines around 5 percent of the fire's 100-mile perimeter by Sunday.

President Donald Trump declared the fire an emergency on Saturday, authorizing federal funds for disaster relief efforts. More than 160 fire departments from California and around the country have been deployed to help quell the week-long blaze.

At the height of its fury on Thursday night, the blaze was whipped into a "fire tornado" by gale-force winds that drove flames across the Sacramento River into the western end of Redding, as thousands of residents fled for their lives in a chaotic evacuation.

BURNING AND LOOTING

Sheriff Bosenko told media that looting in the evacuated neighborhoods was a concern. About 260 National Guard soldiers and about 100 police officers were guarding evacuated homes, he said.

Two people were arrested for attempting to loot three homes, the Shasta County Sheriff's office said.

The community of Keswick, with a population of about 450, was reduced to cinders.

"We have seen really extremely explosive fire behavior on this particular fire, but it's not unique any more to what we are seeing on fires in California," Cal Fire's Anthony said.

Wildfires have scorched almost 4.3 million acres (1.7 million hectares) across the country so far this year, less than last year but more than the 3.7 million-acre (1.5 million-hectare) average for the same period over the last decade.

The Carr Fire is among 17 major fires blazing in California with more than 200,000 acres burning, the National Park Service said.

One of the California fires prompted a rare closure of much of Yosemite National Park last week, while another forced mass evacuations from the mountain resort community of Idyllwild, east of Los Angeles.