A former firefighter accused of starting a wildfire that killed one person and destroyed dozens of homes in rural Northern California has pleaded not guilty to murder and arson.

Powerful winds have pushed a raging wildfire to the doorstep of a wealthy US coastal city, threatening to destroy dozens more homes and leading to the evacuation of more than 20,000 people.

Prosecutors in California are to review evidence before deciding whether to charge a 12-year-old boy whose play with matches started a blaze that ripped through nearly 60 square miles and destroyed 21 homes.

Firefighters were hampered by erratic wind and low humidity today as they made slow progress against a fire that had burned nearly 12,000 acres and four homes in the Northern California wine country.