Evacuation orders also were posted on Sunday for several Napa County neighborhoods, according to the California Department of Forestry and Fire Protection (CalFire).
By 1:30 p.m., flames stoked by strong, gusty winds had scorched some 1,200 acres of rolling hillsides, CalFire said.
There were no immediate reports of injuries, but a Reuters photographer in St. Helena saw a number of structures that had been burned.
The Napa Valley, world renowned as one of California’s premiere wine-producing regions, has been plagued by a series of wildfires outbreaks in and around the Bay area over the past several years.
The latest came as the Pacific Gas and Electric Company announced it was temporarily shutting off power to transmission lines in portions of 16 counties across northern and central California as a precaution against heightened wildfire risks posed by hot, windy, dry conditions.
The public safety power shutoffs were expected to affect some 65,000 homes and businesses in the region, said PG&E, the state’s largest electric utility.
CalFire said a fire weather watch was due to go into effect on Monday across much of Southern California due to a forecast return of hot, gusty Santa Ana winds and low humidity from San Diego to Los Angeles and Ventura counties. (Reporting by Stephen Lam in St. Helena; Additional reporting and writing by Steve Gorman in Los Angeles; Editing by Daniel Wallis)