More than a dozen coroner search and recovery teams looked for human remains from a Northern California wildfire that killed at least 42 – making it the deadliest in state history – as anxious relatives visited shelters and called police hoping to find loved ones alive.

Lisa Jordan drove 1000km from Yakima, Washington, to search for her uncle, Nick Clark, and his wife, Anne Clark, of Paradise, California. Anne Clark suffers from multiple sclerosis and is unable to walk. No one knows if they were able to evacuate, or even if their house still exists, she said.

"I'm staying hopeful," she said. "Until the final word comes, you keep fighting against it."

Butte County Sheriff Kory Honea updated the confirmed fatality number – a figure that is almost certain to spike following the blaze that last week destroyed Paradise, a town of 27,000 about 290km north-east of San Francisco.

Authorities were bringing in two mobile morgue units and requesting 150 search and rescue personnel. Officials were unsure of the exact number of missing.

"I want to recover as many remains as we possibly can, as soon as we can. Because I know the toll it takes on loved ones," Honea said.

Coroner search teams visited dozens of addresses belonging to people reported missing. For those on the grim search, no cars in the driveway is good, one car a little more ominous and multiple burned-out vehicles equals a call for extra vigilance.

State officials said the cause of the inferno was under investigation.

Meanwhile, a landowner near where the blaze began, Betsy Ann Cowley, said she got an email from Pacific Gas & Electric Co. the day before the fire last week telling her that crews needed to come onto her property because the utility's power lines were causing sparks. PG&E had no comment on the email.

More than 8000 firefighters statewide were battling wildfires that destroyed more than 7000 structures and scorched more than 840 sq km, the flames feeding on dry brush and driven by blowtorch winds.