Two years to the day after some of the deadliest wildfires tore through Northern California wine country, a utility announced on Tuesday it will shut off power to more than 800,000 customers in the largest preventive outage in state history - to try to prevent wildfires caused by faulty power lines.

With windy, dry weather in the forecast and warnings of extreme fire danger, Pacific Gas & Electric utility said it will start turning off power to 34 counties in northern and central California after midnight Wednesday.

The Southern California Edison utility website said more than 106,000 of its customers in parts of eight counties could face power cuts.

It may take “several days to fully restore power after the weather passes and safety inspections are completed,” said Michael Lewis, senior vice president of PG&E's electric operations, in statement.

The number of customers and counties affected includes an area of wine country north of San Francisco where several fires two years ago killed 22 people and destroyed thousands of homes.

Wildfires spread across California – in pictures Show all 32 1 /32 Wildfires spread across California – in pictures Wildfires spread across California – in pictures Firefighters battle a blaze at the Salvation Army Camp in Malibu Getty Wildfires spread across California – in pictures Flames from the Camp fire burn near a home atop a ridge near Big Bend AFP/Getty Wildfires spread across California – in pictures Cathy Fallon (centre) who stayed behind to tend to her horses during the Camp Fire, embraces Shawna De Long (left) and April Smith who brought supplies for the horses Reuters Wildfires spread across California – in pictures A helicopter drops flame retardant on a wildfire in Malibu Getty Wildfires spread across California – in pictures An air tanker drops water on the fire along the Ronald Reagan Freeway in Simi Valley AP Wildfires spread across California – in pictures An abandoned car from fleeing residents of Paradise in the Pentz road area EPA Wildfires spread across California – in pictures A firefighter tackles the fire along the Ronald Reagan Freeway in Simi Valley AP Wildfires spread across California – in pictures A Jack In The Box fast food restaurant burns as the Camp fire moves through Paradise, California AFP/Getty Wildfires spread across California – in pictures Yuba and Butte County Sheriff officers label a body bag AFP/Getty Wildfires spread across California – in pictures Firefighters hose down trees on Bell Canyon Road, near Malibu AFP/Getty Wildfires spread across California – in pictures A fire burns at the Salvation Army Camp Getty Wildfires spread across California – in pictures A firefighting DC-10 makes a fire retardant drop over a wildfire in the mountains near Malibu Canyon Road AP Wildfires spread across California – in pictures A house burns in Paradise, California AFP/Getty Wildfires spread across California – in pictures Bins have melted and ballooned in the heat in Magalia, Butte County EPA Wildfires spread across California – in pictures Satellite image taken on 8 November shows plumes of smoke from the Camp Fire stretching across portions of Northern California AFP/Getty Wildfires spread across California – in pictures Firefighters battle the Camp Fire AP Wildfires spread across California – in pictures Firefighters battle the Woolsey Fire Reuters Wildfires spread across California – in pictures Deputy Coroner Justin Sponhaltz, of the Mariposa County Sheriff's Office, recovers human remains found at a home destroyed by the Camp Fire AP Wildfires spread across California – in pictures Buildings burn in Paradise, California EPA Wildfires spread across California – in pictures Local residents bring their horses to Zuma Beach and away from the Woolsey Fire in Malibu Reuters Wildfires spread across California – in pictures A used car dealership burns in Paradise, California Reuters Wildfires spread across California – in pictures Yuba and Butte County Sheriff officers inspect a burned vehicle after discovering remains nearby in Concow AFP/Getty Wildfires spread across California – in pictures Firefighters battle the flames in Thousand Oaks Reuters Wildfires spread across California – in pictures A house burns in Paradise, California AFP/Getty Wildfires spread across California – in pictures A house burns in Paradise, California AP Wildfires spread across California – in pictures Search and rescue teams work to evacuate patients from the burning Feather River Hospital in Paradise, California AFP/Getty Wildfires spread across California – in pictures Embers blow in the wind in Paradise, California AFP/Getty Wildfires spread across California – in pictures In Butte County, the sky is filled with the smoke of the Camp Fire EPA Wildfires spread across California – in pictures Firefighters at work in Thousand Oaks Reuters Wildfires spread across California – in pictures A house burns in Paradise, California AP Wildfires spread across California – in pictures The burned remains of a house and car are left after the Camp Fire in Paradise, California AFP/Getty Wildfires spread across California – in pictures A shop burns in Paradise, California AFP/Getty

San Francisco is the only county in the nine-county San Francisco Bay Area where power will not be affected.

“We're ready to go,” said Jaina French, spokeswoman for the city of Napa. “We're encouraging our community to be as prepared as possible.”

That outage will also affect portions of the agricultural Central Valley, the state's northern and central coasts and the Sierra Nevada foothills where a November wildfire blamed on PG&E transmission lines killed 85 people and devastated the town of Paradise.

Jennifer Siemens, who lost her home in Paradise, rents a house in the nearby town of Oroville and said she is bracing for a third blackout in a month.

Siemens was preparing by having her car gassed up, stocking up with bottled water and flashlights and making sure all of the family's electronic devices were fully charged.

“What's wrong with the power lines that they have to do this so much?” asked Siemens. “We don't want any more fires, obviously, but I feel like they are going a little overboard.”

In Butte County, where Paradise is located, people lined up at gas stations Tuesday morning to fill up their cars and portable containers with fuel for generators. They also rushed to stores to buy flashlights, ice chests and batteries.

PG&E said it planned to update customers by text message and email to Tuesday where and when the power would be cut off. Its website, where people could check whether their addresses would be affected, was down Tuesday afternoon after being overloaded with visitors. In Southern California, the largest numbers of potentially affected customers were in Los Angeles County and to the east in San Bernardino and Riverside counties.

Winds can knock down live wires and power poles or drive trees and other vegetation into contact with them — and some of California's most destructive blazes in recent years were started by PG&E power lines.

But the potential planned outages will not be limited to fire-prone areas because the utilities must turn off entire distribution and transmission lines to much wider areas to minimise the risk of wildfires.

Public agencies throughout the region were urging people to prepare by buying water and non-perishable food, getting a full tank of gas, having cash at hand and parking vehicles outside garages or making sure they know how to manually open their garage doors.

The California Department of Forestry and Fire Prevention said it increased staffing in preparation for extreme fire weather and what was expected to be the strongest wind event so far this fire season.

“With some of the most destructive and deadliest fires occurring October through December, we need Californians to not be complacent,” said California Fire Chief Thom Porter in a news release. “Residents need to be ready to evacuate at a moment's notice in the event of a wildfire.”

In the San Francisco Bay Area, Sonoma County Sheriff's Sergeant Juan Valencia said his office was ready to notify residents of outages through emergency alerts and social media as soon as it received word.

“We don't know what the extent of the public safety and power shut-off is going to be, so we're just going to have to adapt,” he said Tuesday.

Oakland Mayor Libby Schaaf asked residents Tuesday not to clog 911 lines with non-emergencies and urged people to be prepared. In 1991, a grass fire torched the Oakland Hills, killing 25 people and destroying more than 3,000 homes. The city cancelled all officers' days off in preparation for the outages.

“We all know the devastation that fires can cause,” she said.

At the Dollar General store in Paradise, people were buying candles, gas cans, ice, flashlights, batteries and canned food and the store ran out of ice chests Tuesday morning, said manager Ben Humphries.

Humphries, who moved to Oroville with his family after losing his home in Paradise, said his family lost power two times already in the last month and he was making sure they had enough fuel for their generator and plenty of ice in coolers.

But he said there was a sense of irony to PG&E's aggressive action in the area now, after the company opted to not to turn off the power ahead of the November 8 fire that wiped out the town of Paradise.

“I understand their concerns but in my opinion it's too little too late, we already had our town burned to the ground,” Humphries said.