SAN FRANCISCO (AP) — A carelessly discarded cigarette, a downed power line, a car's backfire or a chainsaw's pull. Just about anything could have started any one of the wildfires now tearing through Northern California, authorities said.

"Every spark is going to ignite a fire," said Ken Pimlott, the state's top firefighter. He said the risk remains "extreme for new starts."

Pimlott said Tuesday that investigators are looking into the causes, but no determination has been made at any of the sites of major wildfires blazing in Northern California. Authorities said 22 were burning Wednesday.

Pimlott, the California Department of Forestry and Fire Protection director, 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 23 people so far.