"Due to the burn injuries, identification could not be immediately made" on the bodies, the sheriff's office said. "Autopsies will be conducted to determine the circumstances of the deaths and to begin the identification process."

The fire also injured three firefighters but the total casualty picture was not yet clear. Nervous relatives posted on Twitter or called 911 dispatchers hoping to find loved ones behind the fire line.

Cal Fire said the fire destroyed an estimated 2,000 structures, including a large swath of the town of Paradise. Another 15,000 are threatened.

Officials evacuated some 30,000 people in the region, including in Magalia, Concow, Butte Creek Canyon and Butte Valley. Three shelters have been set up, but officials said at least one is already full.

"The town is devastated, everything is destroyed," California Department of Forestry and Fire Protection Capt. Scott McLean told NBC News. "There's nothing much left standing."

"We were engulfed in flames," Butte County Supervisor Doug Teeter said. "I don't know what we are coming back to after this. Probably a moonscape. As we drove out, homes were burnt to the ground."

Cal Fire said nearly 2,300 firefighters, 300 fire trucks and 11 helicopters were fighting the flames. Several Paradise businesses have been destroyed, including a fast food restaurant, a diner and a church.

Officials said strong winds are making it difficult for air tankers to extinguish the flames.

"In the past few years, just the way fires have moved, firefighters have had to help with evacuations before they can go back in to put out the fire," Cal Fire spokesperson Lynne Tolmachoff said, according to the San Francisco Chronicle. "There's pretty much complete devastation in that community--entire streets where houses are wiped out."

The cause of the fire is unknown.

In Southern California, officials said the Woolsey Fire forced the entire city of Malibu to evacuate Friday. The flames threatened affluent neighborhoods in Malibu Canyon and Agoura Hills.

"The wind-whipped conditions ... this is ripe conditions for explosive fire behavior," Los Angeles Fire Capt. Erik Scott told NBC News. "This is the new normal. When we have conditions like this, when it's such incredible wind, that brings us into a different caliber, so it's become a more challenging condition."

The Woolsey Fire started in Simi Valley Thursday, where it destroyed about 30 homes and burned 8,000 acres by early Friday.

Los Angeles County Fire Department Chief Trey Epsy said crews created "water curtains" between homes to salvage the ones they could.

"They will continue to save homes and do whatever they can until the work is done," Epsy told KCBS-TV.

Officials said the mandatory evacuations clogged the roads in Oak Park, making it difficult to escape.

"It's been a roller coaster," one resident who stayed with his house told KCBS. "Hopefully they're able to get it under control and save this neighborhood."

Another neighbor said the fire was "like a freight train" and praised firefighters for saving so many homes.

Pepperdine University in Malibu, which had several students at the deadly Thousand Oaks shooting Wednesday night, canceled classes Friday because of the approaching fire.

A third blaze called the Hill Fire was threatening Thousand Oaks, where a mandatory evacuation has been ordered for part of the city. The Hill Fire has gone over many of the same areas that burned in 2013. The Point Nagu Naval Base, Camarillo Springs and California State University Channel Islands all have mandatory evacuations.