A home burns as the Camp Fire moves through the area on November 8, 2018 in Paradise, California.

Rescue teams sifted through burned homes and vehicles on Friday for the remains of victims in the northern California town of Paradise, as the number of those missing in the state's deadliest wildfire spiked to 630 people.

At least 63 people were killed in and around Paradise, which was virtually incinerated by the Camp Fire, a blaze that erupted Nov. 8 in the Sierra foothills 175 miles (280 km) north of San Francisco. The fire is among the deadliest to have hit the United States over the last century.

Authorities attribute the death toll partly to the speed with which flames raced through the town of 27,000, driven by wind and fueled by desiccated scrub and trees.

Butte County Sheriff Kory Honea said on Thursday the remains of seven further victims had been located since Wednesday's tally of 56. The number of missing jumped to 630 people late Thursday from 130 the previous night.

Many of those initially reported as missing have been found alive, so Honea emphasized Thursday that the list of missing would fluctuate as new people were reported missing or others turned up safe.

Paradise resident Wayne Williamson lost his home, car and belongings in the fire and is now looking for his brother Ronald Crawford, who has not been heard from since before the fire.

"He hasn't showed up yet and I think he would by now," Williamson told KRCR TV. "It's getting to the point where I am going to have to reach out and ask for help."

Many of those listed as missing are over the age of 65. Local officials and realtors have sold Paradise as an ideal place to retire.

Relatives of retired U.S. Navy veteran David Marbury, 66, are waiting to hear from him. No one has managed to speak with him since the wildfire began, and relatives' phone calls have gone directly to his voicemail.

Marbury moved to Paradise a few years ago because he liked to be by himself, relatives said.

On Thursday, Marbury's landlord confirmed to relatives that his duplex in Paradise had burned down. Sheriff's officials told them his car was still in the garage.

"I really hope he's still alive and we're going to be able to see him," Marbury's niece Sadia Quint, 30, told Reuters by phone. "We just hope that he's still with us."

Nearly 12,000 homes and buildings burned hours after the blaze erupted, the California Department of Forestry and Fire Protection (Cal Fire) said.

Thousands of additional structures remain threatened as firefighters, many from distant states, labor to contain and suppress the flames.