Northern California residents left homeless by the deadliest, most destructive wildfire in state history braced for a new bout of misery on Wednesday from showers expected to plunge encampments of evacuees into rain-soaked fields of mud.

As much as 20cm of rain is forecast to fall by Friday in areas around the town of Paradise, a community of nearly 27,000 people about 280km northeast of San Francisco that was largely incinerated by the blaze, known as the Camp Fire.

The Northern California sheriff said two more people had been confirmed dead in the fire, bringing the death toll to 83 with more than 560 still missing.

The storm will help firefighters still battling the fire, but will add to the suffering of the residents left homeless by the disaster. Some of them, whose numbers have not been determined, are camping out rather than staying in emergency shelters.

The toll in the deadliest wildfires in recent California history climbed to 81 [Josh Edelson/AFP]

Kelly Boyer, who lost his home in Paradise, has been sharing a tent with a friend outside a Walmart store in nearby Chico, where overnight low temperatures have fallen to just above freezing.

Boyer has received wooden pallets and plastic tarps donated by local residents to keep his tent off the ground and dry, but he said the rain would still make a mess.

“It’s going to be mud city,” he told Reuters news agency.

‘Scared they’ll be washed away’

There’s also fear the rains may wash away the remains of those who have not yet been identified.

“I’m scared,” Paradise resident Deborah Laughlin told the Los Angeles Times.

The 63-year-old lost her home and is still searching for her son and his pregnant wife. She last heard from them when the couple evacuated earlier this month, the LA Times reported.

“I’m scared they’ll be washed away and people’s remains will never be found,” she said.

Forecasters said the rain, which in some areas is likely to be accompanied by strong winds, might also cause rivers of mud and debris to slide down flame-scorched slopes stripped of vegetation.

A search and rescue dog searches for human remains after the Camp Fire [John Locher/AP Photo]

The fire has burned across 61,000 hectares of the Sierra foothills.

Mass evacuations since the fire erupted on November 8 have, however, removed most people from any debris flow, according to National Weather Service (NWS) hydrologist Cindy Matthews.

She said the volcanic soil and relatively shallow slopes in the fire zone also mean the ground is unlikely to become saturated enough for hillsides to give way to landslides.

Ryan Spainhower and his wife, Kimberly, weep after finding a coin they had made during their honeymoon amidst the ashes of their home in Paradise [Josh Edelson/AFP]

However, authorities in Southern California warned residents in areas burned by wildfires in the foothills and mountains northwest of Los Angeles of mud-flow hazards from rain this week. One of those blazes, the Woolsey Fire, killed three people.

Evacuees also face increasingly chilly weather.

“It’s real cold at night,” evacuee Mark Kempton told KRCR TV. He said he was going to sleep in his car instead of a tent to stay warm.

Anna and William Goodnight, of Paradise, sit outside their tent at a makeshift evacuation centre for displaced people [Terray Sylvester/Reuters]

Smoke from the fires has drifted across the country to the East Coast, where it left a brownish-orange haze that was credited with causing unusually vibrant sunsets on Monday.

The cause of the Camp and Woolsey fires is under investigation, but electric utilities reported equipment problems around the time both blazes broke out.