Of the 65 victims, 63 were killed in Northern California's Camp Fire, deemed as the worst wildfire in the state's history, while two other people were killed in Southern California's Woolsey Fire, reports CNN.

Butte County Sheriff and Coroner Kory Honea said on Thursday evening that hundreds of rescue personnel -- deputies, National Guard troops and coroners -- dressed in white overalls sifted through smouldering rubble and checked mangled cars, searching for human remains.

Camp Fire has turned the hard-hit town of Paradise into ash and debris and also devastated the nearby communities of Magalia and Concow.

Honea has invited relatives of the missing so that authorities could collect DNA samples from them.

The DNA will be used to help identify the victims.

More than 9,600 firefighters, including many from out of state, were battling wildfires across California.

By Thursday, Camp Fire, which has destroyed about 9,700 homes and scorched 141,000 acres in Northern California, was 40 per cent contained.

The Woolsey Fire, which like the Camp Fire began on November 8, has burned more than 98,000 acres and destroyed more than 500 structures.

It was 62 per cent contained.

More than 230,000 acres burned in California in the past week. That's larger than the cities of Chicago and Boston combined.

President Donald Trump is slated to visit the region on Saturday.