At least 11 people have been killed, and more than 1,500 structures have been destroyed as wildfires that sweep across Northern California.

California Governor Jerry Brown declared a state of emergency in Napa, Sonoma and Yuba counties.

Among those killed were a couple aged 99 and 100 years who had been married for 75 years, according to local media.

Scott McLean, the deputy chief of the California Department of Forestry and Fire Protection (Cal Fire), told NBC's Today show that his department hoped to "start seeing some turnaround throughout the course of today and into tomorrow".