A wildfire that moved so fast that firefighters couldn't hope to stop it quadrupled in size on Friday after destroying several thousand buildings and levelling much of a Northern California town of nearly 30,000 people, authorities said.

The blaze has so far killed at least 11 people among them five were found in vehicles that were torched by the flames of a ferocious wildfire.

The fire has grown to nearly 285 sq km.

Paradise is 289km northeast of San Francisco.

The director of the California Governor's Office of Emergency Services, Mark Ghilarducci said the magnitude of the destruction is unbelievable and heartbreaking.

Officials said fires across California have forced 157,000 people from their homes.

Authorities issued mandatory evacuation orders for tens of thousands of people in the scenic area in the foothills of the Sierra Nevada mountains, including some residents of Chico, population 93,000, near Paradise.

Fanned by strong winds, the so-called "Camp Fire" has burned 20,000 acres and has not been contained, the California Fire Department (Cal Fire) said.

Acting California Governor Gavin Newsom declared a state of emergency to provide assistance to the fire-hit areas.

A Cal Fire spokesman said around 1,000 buildings were believed to have been destroyed in Paradise. Among those evacuated were all of the patients at the Feather River Hospital in Paradise.

More than 2,200 firefighters were battling the blaze supported by helicopters and water tankers.