WASHINGTON - The death toll from flooding in the US state of West Virginia rose to 24, as President Barack Obama declared a major disaster, releasing federal aid for some of the hardest-hit areas.

The president "ordered federal aid to supplement state and local recovery efforts in the area affected by severe storms, flooding, landslides and mudslides," the White House said in a statement.

Days of heavy rain have caused massive flooding in the state, where high waters have washed away cars, trapped hundreds and cut power to large areas.

More than 21,300 people were without power across the state Saturday evening according to the West Virginia Division of Homeland Security and Emergency Management. Hundreds of homes had been severely damaged or destroyed and more than 60 roads remained closed, it said.

Photos on the division's Facebook page showed a muddy, swollen river in the West Virginia town of Clendenin that had spilled over its banks and inundated a nearby neighbourhood with floodwater.

Meanwhile, California firefighters on Sunday struggled to contain a wildfire that killed at least two people and destroyed some 150 homes as it raced over drought-parched land whipped up by strong wind.

The blaze, known as the Erskine Fire, is raging in an agricultural and oil region of south-central California.

The blaze has spread to nearly 37,000 acres (15,000 hectares), the California Department of Forestry and Fire Protection (CAL Fire) said.

Some 1,700 personnel have been assigned to battle the wildfire, which is just 10 percent contained, CAL Fire said on Twitter. At least 75 other homes have fire damage, officials said.

Unusually high temperatures, bone-dry conditions that make brush and grass flammable, and powerful winds gusting up to 50 and even 60 miles per hour (80 to 100 kilometers per hour) helped spread the flames of a fire that broke out Thursday afternoon in the sparsely populated Lake Isabella area of Kern County. Deputies from the Kern County Sheriff's office said they may have found the remains of a third person killed by the fire in the victim's mobile home in the Lake Isabella area.

"We've located what we believe are human remains," sheriff's spokesman Ray Pruitt told reporters on Saturday. "We are treating it like a crime scene."

Pruitt said the remains were "pretty badly burned."

The cause of the fire is still unknown, but if investigators determine that it was intentionally set then the fire deaths will be treated as homicides, Pruitt said.

Firefighters are having an especially hard time battling the blaze due to rough hills in the area.

"This is very, very steep terrain," CAL Fire Battalion Chief Mike Mohler said in video posted on Facebook, as he pointed towards the smoke.

"We're looking at increased winds ... high temperatures, low humidity in the single digits - that makes this a very difficult firefight," Mohler said.

The National Weather Service forecast low humidity and a temperature of 99 degrees Fahrenheit (37.2 degrees Celsius) on Sunday, unusually hot for this time of the year in that region of California.

Thousands of area residents affected by the fire have been evacuated to shelters run by groups like the American Red Cross.

"I've lost everything - all I have is what I've got on," local resident Fred Coleman told CBS 5KPIX television, interviewed at an evacuation center in the town of Kernville.

California Governor Jerry Brown has issued a state of emergency for the region, allowing aid to be deployed more quickly.

Authorities have closed several highways and evacuated two schools and a retirement home in the affected area.

California is experiencing a record five-year drought and trees and brush are at risk of igniting from the smallest spark.

More than 14 large fires are currently raging in the United States, mostly in the southwest, where a record heat wave left at least five dead last Sunday.