LOS ANGELES — With devastating wildfires becoming more frequent in California, power companies have found themselves on the defensive. Their equipment has been singled out as a frequent culprit. Now, to reduce the hazard, they are pulling out a rarely used tool: the blackout.

Power for tens of thousands of Northern Californians was cut Sunday as high winds prompted fire alerts in a region hit hard by fires a year ago — including parts of Napa and Sonoma Counties, the state’s leading wine area.

The action was taken by Pacific Gas and Electric, whose territory covers most of central and Northern California. PG&E and Southern California Edison warned tens of thousands of others that they, too, could face imminent blackouts.

Officials said they were acting purely for safety reasons. “We’ve always had this as a tool,” said Phil Herrington, senior vice president for transmission and distribution at Southern California Edison. “Based on our experience, based on our view, the wildfire threat is increasing.”