At least 63 people have died in a Northern California wildfire while 631 people are sill unaccounted for, authorities have said.

Butte County Sheriff Kory Honea revealed the increased missing persons total at a news conference on Thursday, having put the figure at 130 just a day earlier.

Honea said the original total was a partial count, and that after authorities went back through all emergency calls and other reports of missing people from the past week, they came up with the new number.

The list probably included some who had fled the blaze and did not realise they had been reported missing, he added.

“The chaos that we were dealing with was extraordinary,” he said of the early crisis hours. “Now we’re trying to go back out and make sure that we’re accounting for everyone.”

Authorities also reported seven more fatalities, bringing the total to 63, in the deadliest wildfire in state history.

Ten years ago, as two wildfires advanced on the town of Paradise, residents jumped into their vehicles to flee and got stuck in gridlock. That led authorities to devise a staggered evacuation plan — one that they used when fire came again last week.

But Paradise’s carefully laid plans quickly devolved into a panicked exodus.

Some survivors said that by the time they got warnings, the flames were already extremely close, and they barely escaped with their lives. Others said they received no warnings at all.

Now authorities are facing questions over whether they took the right approach.

Reeny Victoria Breevaart, who lives in Magalia, a forested community of 11,000 people north of Paradise, said she could not receive warnings because mobile phones were not working. She also lost electrical power.

Honea said evacuation orders were issued through 5,227 emails, 25,643 phone calls and 5,445 texts, in addition to social media and the use of loudspeakers. As mobile phone service went down, authorities went into neighbourhoods with bullhorns to tell people to leave.

“The fact that we have thousands and thousands of people in shelters would clearly indicate that we were able to notify a significant number of people,” the sheriff said.

On Thursday, firefighters reported progress in battling the nearly 220-square-mile blaze that displaced 52,000 people and destroyed more than 9,500 homes. It was 40 percent contained, fire officials said.

California Army National Guard members, wearing white jumpsuits, looked for human remains in the burned rubble, among more than 450 rescue workers assigned to the task.

President Donald Trump plans to travel to California on Saturday to visit victims of the wildfires burning at both ends of the state.

In Southern California, crews continued to gain ground against a blaze of more than 153 square miles that destroyed more than 500 structures in Malibu and communities. At least three deaths were reported.