All five victims were found in the same area of the town of Paradise, in the north of the state.
Sheriff Korey Honea said reports of more deaths are being investigated.
In a statement, the Butte County Sheriff's Office said: "The preliminary investigation revealed that the victims were located in vehicles that were overcome by the Camp Fire."
California fire captain Scott McLean said earlier that "pretty much the entire community of Paradise is destroyed", adding that the fire had grown to almost 110 square miles - four times its original size.
A separate fire is threatening Malibu and has caused the city to be evacuated.
Those who live there have been warned of an "imminent threat" to their safety, with thousands of people being urged to flee however they can.
"It is critical that residents pay close attention to evacuation orders," the Los Angeles County Fire Department tweeted.
"This is a very dangerous wind driven fire."
US media reports that schools have also been closed and evacuated due to the fire, and animals have been moved out of the LA Zoo in Griffith Park.
No deaths have been reported in Malibu.
Rapper Kanye West and his wife Kim Kardashian West are among those who have taken to social media to confirm that they are safe.
View this post on Instagram
A post shared by Gary Nuell (@garynuell) on
The first of the fires broke out on Thursday, northwest of Los Angeles, and roared south, with an estimated 75,000 homes evacuated in western Los Angeles County and eastern Ventura County.
Malibu has about 13,000 residents - including a number of celebrities - and many have shared pictures of busy roads as scores of cars take to the roads in a bid to escape.
The LA County Sheriff's Office said it was receiving "many emergent phone calls" from people who "need our help to evacuate" and urged motorists in the area to be aware of emergency vehicles.
Strong blustery winds combined with dry conditions have helped the blaze spread, after weeks without rain and low humidity at the height of the wildfire season in north California.
More than 50,000 people have signed Sky News' petition backing televised leaders' debates for elections - have you?
In the San Francisco Bay area, some 180 miles away from Paradise, locals have been encouraged to stay indoors due to worsening air quality caused by smoke from the fire.
More from California
Thousand Oaks shooting: The victims of California bar attack
Thousand Oaks residents know latest mass shooting unlikely to change US gun laws
Thousand Oaks shooting: Gunman who killed 12 at bar was ex-marine and Afghanistan veteran
US midterms: How California could prove key for the Democratic Party
Robert Durst of The Jinx to stand trial for murder after TV documentary about his life
Death row prisoner Jonathan Fajardo 'killed by fellow condemned inmate'
The air has become hazy and the smell of smoke is overwhelming, prompting officials to declare it unhealthy.
They are advising older people and children to relocate any planned physical activities indoors.