Ten people were killed Monday as wildfires raged across eight counties in Northern California, state officials said.

The California Department of Forestry and Fire Protection confirmed two deaths in Napa County and another in Mendocino County.

Some 1,500 structures have been destroyed and more than 103,000 people are without gas and electricity, while at least 20,000 residents have been forced from their homes, authorities said.

California Gov. Jerry Brown declared a state of emergency in the counties affected by the blazes.

"This is really serious. It's moving fast. The heat, the lack of humidity and the winds are all driving a very dangerous situation and making it worse," he told a press conference. "It's not under control by any means. But we're on it in the best way we know how."

A half-dozen school districts canceled classes on Monday.