Auto insurers were already bracing for another bad year when the downpour started in Texas, producing potentially hundreds of thousands of new claims.

“We do know that approximately 100,000 claims have come in” as of Thursday, said Matt Stillwell, manager of governmental and regulatory communications at the Insurance Council of Texas, a trade association. He said the number was expected to climb as high as 500,000.

“It is looking to be a huge impact on the auto insurance market,” he said.

While homeowners’ insurance policies almost always exclude flood damage, comprehensive auto policies do cover flooding. The typical household in Houston has two cars, and Mayor Sylvester Turner urged residents to “hunker down” as Hurricane Harvey made landfall, hoping to avoid a replay of the tie-ups and crashes that killed about 100 people fleeing Hurricane Rita in 2005.

That means few people moved their cars out of harm’s way before the flooding started. Texas drivers are not required to have comprehensive auto insurance — the type that covers flood and other types of damage. People holding only the legally required insurance — liability coverage for damage done to other people’s cars — will not have valid claims, Mr. Stillwell said.

Those who have comprehensive insurance should get a payment based on replacement value minus depreciation, if their car is a total loss.

For insurers, the losses will affect some more than others. The big, household-name auto insurers “have sufficient geographic and product diversification to absorb the losses,” S&P Global Market Intelligence said in a report on the impact of the storm and flooding on various parts of the insurance industry.

But “some of the regional and local players could face significant hits to their earnings, and possibly their capital,” the ratings firm added.

As a possible example, it cited Hochheim Prairie Insurance, a mutual insurer that does business solely in Texas, offering auto insurance and other personal lines. Mutual insurers are owned by their policyholders and do not issue stock in the public markets, so they cannot raise fresh capital by selling new shares.

Pam Lahodney, a vice president of marketing and underwriting at Hochheim, said in an email that it was too early for the company to assess the financial effects of the storm on its business. “At this time, our focus is to provide assistance to those members impacted by Hurricane Harvey,” she said.

State Farm Mutual Automobile Insurance, Allstate Insurance, Farmers Insurance Exchange, National Indemnity Company (an affiliate of Geico), the Progressive Group, and Metropolitan Property and Casualty Insurance (a unit of MetLife) are among the big companies that write a large portion of their auto insurance business in Texas.

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