Redding, a city of 92,000 near the OR border, is at grave risk from the Carr fire, which has so far killed two people.
One person was killed in a raging, out-of-control wildfire that sent residents racing to flee a northern California city on Friday as flames burned homes and businesses and knocked out power, fire officials said.
Firefighters and police "went into life-safety mode", hustling door to door to usher civilians out of harm's way, said Scott McLean, a spokesman for the California Department of Forestry and Fire Protection (CalFire).
The fire rapidly expanded Thursday when erratic flames swept through the historic Gold Rush town of Shasta and nearby Keswick, then cast the Sacramento River in an orange glow as they jumped the banks into Redding. "There was not much of a warning".
Hospital staff is preparing to evacuate the facility if needed, a Cal Fire spokesman said.
Weather conditions are exacerbating the fire, with hot and windy weather fanning the flames, causing the wall of fire to grow larger.
As the Carr fire burned through Shasta Co., wildfires scorched several other parts of the state.
Parts of Redding, which has about 92,000 residents and is the largest city in the region, also have been evacuated.
KRCR, a Redding TV station and CNN affiliate, interrupted its newscast and evacuated its facility Thursday night as the fire approached. Two people so far - a Redding firefighter and a private bulldozer operator - have died.
"Right now, we are being evacuated", anchor Allison Woods said during Thursday night's broadcast. The Ferguson Fire near Yosemite National Park, which has charred 45,911 acres (18,500 hectares), was 29 percent contained.
About 100 homes were still under threat in the San Francisco Bay community of Clayton, although firefighters had stopped the progress of a small fire there after one house burned.
Some 1,750 firefighters are battling the blaze, Cal Fire said.
The state governor, Jerry Brown, has declared a state of emergency in northern California's Shasta county, and in southern California's Riverside county, to help provide local fire crews with the resources they need to battle the blazes.
A 32-year-old man is under arrest, booked on five counts of arson.
This year so far, nearly 4 million acres (1.6 million hectares) have been blackened by wildfires, above a 10-year average of 3.6 million acres (1.5 million hectares) over the same period, according to the National Interagency Fire Center.
Hundreds of miles to the south, the Cranston Fire grew to 7.5 square miles (19 square kilometers) and about 3,000 residents remained under evacuation orders in Idyllwild and several neighboring communities.