Fast-moving fires and shifting winds have forced thousands more Californians to evacuate their homes, as the death toll from the state’s deadliest blaze in history increases to at least 40.

More than 11,000 firefighters struggled to contain 16 major wildfires that have ravaged Northern California for a week on Saturday (local time), scorching 220,000 acres and destroying 5700 structures since flames first stoked on October 8.

Since then, 40 fatalities have been confirmed and more than 200 people are still missing as some 100,000 residents have been forced from their homes, including 3000 evacuated on Saturday (local time) from the city of Santa Rosa.

The fires’ death toll surpassed the 29 deaths from the Griffith Park fire of 1933 in Los Angeles.

“This is truly one of the greatest tragedies that California has ever faced. The devastation is just unbelievable. It is a horror that no one could have imagined,” California Governor Jerry Brown said on Saturday during a visit to a devastated Santa Rosa.

Winds are expected to weaken on Sunday, which should help in fighting the fires but high temperatures and dry conditions could continue to transform grass and vegetation into fuel, officials warned.

Firefighters from states including Oregon, Washington, Arizona, Colorado and Nevada have joined crews from California to battle the blazes.

Firefighting efforts include 880 fire engines, 134 bulldozers, 70 helicopters and a 14 air tankers to conduct water drops, according to local officials.

Whole neighbourhoods of Santa Rosa have been reduced to landscapes of ash, smouldering debris and burned-out vehicles.

Some victims were asleep when flames engulfed their homes, and many survivors had only minutes to flee.

With 235 people still missing on Saturday in Sonoma County alone, and rubble from thousands of incinerated dwellings yet to be searched, authorities have said the number of fatalities from the North Bay fires would likely climb.

-with AAP