SAN FRANCISCO (CBSNewYork/AP) — Authorities say just about anything could have started any one of the wildfires now tearing through Northern California.

Fire officials have not yet determined the cause of any of the 17 major fires burning north of San Francisco.

“Every spark is going to ignite a fire,” the state’s top firefighter, Ken Pimlott, said, adding that the risk remains “extreme for new starts.”

Pimlott said “98 percent” of all wildfires are started by people and it’s unlikely lightning is to blame for any of the fires that exploded overnight Sunday, killing at least 21 people so far. The wildfires already rank among the deadliest in California history, and officials expected the death toll to increase as the scope of destruction becomes clear.

“Make no mistake — this is a serious, critical, catastrophic event,” said Pimlott.

Among those killed were a 100-year-old man and his 98-year-old wife.

Charles and Sara Rippey were married for 75 years and died together when the fire reached their home.

“It hit so fast and they just didn’t have a chance,” their son, Mike, said. “My mother had a stroke and she couldn’t move very well at all and my father certainly never would have left her.”

Nearly 700 people are still reported missing.

None of the major fires has been contained. They are spread over a 200-mile region north of San Francisco from Napa in the south to Redding in the north, taxing firefighting resources.

The biggest and most devastating fire is burning in Santa Rosa, a city of 175,000 people 45 miles north of San Francisco. A fire there swept through several neighborhoods and business districts, destroying at least 550 homes and 21 commercial buildings. Many residents had only minutes to flee.

Nine-year-old Lilly Biagini and her mother were away from their Santa Rosa home Sunday night before the fire broke out and were unable to return.

“I lost my legs. I lost everything,” said Lilly, whose prosthetic legs were inside the home. “They’re really important to me. They’re a lot of money.”

The firefighting effort is likely to become more complicated in Santa Rosa, as gusty winds are in the forecast.

“We’re working very diligently. These are very extreme conditions,” Cal Fire Battalion Chief Kurt Van Wormer said.

In Solano County, crews were raking grass and setting back fires, hoping to steer the flames away from homes.

“It’s all about life saving and evacuations,” Sheriff Rob Giordano said. “My advice to those of you who are advised is go.”

California Office of Emergency Services director Mark Ghilarducci said more than 4,000 firefighters, law enforcement officials and others are responding. Airplanes are dropping fire retardant and fresh firefighters from Southern California and Nevada are streaming in to help. Lines are being dug on the south side of many blazes in preparation for northerly winds picking up.

At least 170,000 acres have been scorched, more than 3,500 homes and businesses have been destroyed, and one trade group says five of its wineries have also been destroyed or seriously damaged. The wine industry in Sonoma and Napa Valley employs more than 50,000 people.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)

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