Amid a rapidly spreading Northern California wildfire, Gov. Jerry Brown (D) declared a state of emergency for Lake and Napa counties.

The Valley Fire began Saturday afternoon about 100 miles north of San Francisco. By Sunday morning, it had burned more than 40,000 acres, according to the California Department of Forestry and Fire Protection.

Hundreds of firefighters worked overnight to try to contain the flames and save homes. Several towns in the fire’s path were under mandatory evacuation orders on Saturday.

Four firefighters suffered second-degree burns, the agency said. They were hospitalized and are in stable condition at the University of California at Davis Medical Center.

More than 5,000 residences are without power, the fire department said, and an unconfirmed number of structures have been destroyed.

California firefighters are also battling another massive blaze, the Butte Fire, about 70 miles southeast of Sacramento. That fire has been raging since Wednesday and is 20 percent contained. It has destroyed 86 homes and 51 outbuildings.