US President Donald Trump expressed sadness Saturday at the devastation in a California town, as more than 1,000 people remain listed as missing in the worst-ever wildfire to hit the US state.

Two huge blazes have created a serious smoke problem across vast areas in the state, and when Trump stepped out of Air Force One at Beale Air Force Base north of capital city Sacramento, the sun was struggling to cut through haze so dense it covered the base like a fog.

Mr Trump landed at Beale Air Force Base just north of Sacramento and shook hands with Governor Jerry Brown and Gov-elect Gavin Newsom on the tarmac. The Democrats joined the president as he visits burned areas and meets with first responders.

“We’ve never seen anything like this in California, we’ve never seen anything like this yet. It’s like total devastation,” Trump said as he stood amid the ruins of Paradise, burned to the ground by a wildfire the president called “this monster.”

Along his drive, several signs thanked Trump for coming but one called him a “moron.” In Chico, near Paradise, Trump met with firefighters and other first responders at makeshift headquarters for emergency services.

“This is very sad,” Trump said after surveying the remains of Paradise, where nearly the only people out on the road were emergency services workers, surrounded by the twisted remains of the incinerated town.

“They’re telling me this is not as bad as some areas; some areas are even beyond this, they’re just charred,” he added after looking at a street lined with melted cars, tree stumps and the foundations of wrecked houses.

Trump studied a huge map spread across a table showing where fires continue to burn.

Keeping alive an earlier controversy, Trump repeated his claim that California had mismanaged its forests and was largely to blame for the fires.

“I’m committed to make sure that we get all of this cleaned out and protected, (we’ve) got to take care of the forest, it’s very important,” Trump said in Paradise.

Brian Rice, president of California Professional Firefighters, called Trump’s earlier remarks “ill-informed,” noting the federal government had cut spending on forest management.

Asked if he believed climate change had played any role in the fires, Trump again pointed to the forest “management factor” and insisted that his “strong opinion” -- he has been skeptical of man’s role in global warming -- remained unchanged.

The deadliest and most destructive wildfire in California’s history, the so-called Camp Fire, has now claimed 76 lives.

The fire has devoured an area roughly the size of Chicago, destroying nearly 10,000 homes and 2,400 other buildings.

Forensic recovery teams continue searching for victims in the charred wreckage of the northern California town of Paradise.

Before returning to Washington, Trump met briefly at an airport hangar with families and first responders touched by the shooting at the Borderline Bar & Grill in Thousand Oaks, which left 12 dead in what Trump called “a horrible, horrible event.” Reporters and photographers were not allowed to accompany the president to the session, which Trump later described as emotional. “What can you say other than it’s so sad to see. These are great people. Great families, torn apart,” he told reporters. “We just hugged them and we kissed them - and everybody. And it was very warm.” He added: “It was tragic and yet in one way it was a very beautiful moment.”

The disaster already ranks among the deadliest US wildfires since the turn of the last century.

Eighty-seven people perished in the Big Burn firestorm that swept the Northern Rockies in August of 1910. Minnesota’s Cloquet Fire in October of 1918 killed 450.

Butte County Sheriff Kory Honea told reporters the number of people unaccounted for had soared, from 631 to 1,011, in 24 hours as authorities received more reports of people missing, and after earlier emergency calls were reviewed.

“I want you to understand that this is a dynamic list,” Honea told reporters, noting there could be duplicates and some people who had escaped could be unaware they were listed as missing.

More than a week later, firefighters have managed to carve containment lines around 45 per cent of the blaze’s perimeter. The fire covered 57,000 hectares, fire officials said.

Besides the toll on human life, property losses from the blaze make it the most destructive in California history, posing the additional challenge of providing long-term shelter for many thousands of displaced residents.

With more than 9800 homes up in smoke, many refugees have taken up temporary residence with friends and family, while others have pitched tents or were camping out of their vehicles.

At least 1100 evacuees were being housed in 14 emergency shelters set up in churches, schools and community centres around the region, with a total of more than 47,000 people remaining under evacuation orders.