Jasper Cooper, senior credit officer for Moody's Ratings, expected insured losses to amount to billions of dollars given the area's high values of homes and businesses.
Homeowners have found it tough to buy insurance in catastrophe-prone states as several firms have pulled out of the market.
"These events will continue to have widespread, negative impacts for the state’s broader insurance market," said Denise Rappmund, senior analyst at Moody's.
"Increased recovery costs will likely drive up premiums and may reduce property insurance availability.”
Morningstar DBRS also said a larger than usual portion of the losses could be uninsured or covered under the California FAIR plan, designed to help homeowners where standard insurance is not available.
JPMorgan on Thursday estimated insured losses at $20 billion, Thomson Reuters publication The Insurer reported, double its estimates of a day earlier due to an escalation of the damage.
