One million Californians have fled deadly, out-of-control wildfires in the largest mass evacuation in the state's 157-year history. The relief effort is shaping up as the biggest and costliest since Hurricane Katrina.

Two people were confirmed dead and more than 50 injured, as 7,000 firefighters battled to save lives and property threatened by the chain of blazes that has charred 600,000 acres and destroyed 1,800 homes and businesses.

As the effort to control the fires entered its fourth day, insurance industry experts began to offer cautious estimates of the costs of the catastrophe. The Insurance Information Institute was the first major trade group to issue a "preliminary" insured-loss estimate.

"Given losses to date, the largely uncontrolled nature of the fire, and experience with past events," said Loretta Worters, vice president of the institute, "insured damages from the California wildfires could exceed $500 million."

Worters said that estimate includes not only damaged and destroyed homes, but also "payments for additional living expenses, losses to businesses, including business interruption insurance, and wind and smoke damage."

Several experts interviewed by Portfolio.com said that the final insurance industry liability from the fires will far exceed $500 million, but few were willing to issue explicit predictions Tuesday, as the crisis worsened in real time.

Neena Saith, an analyst with the insurance consulting firm Risk Management Solutions, said that the firm was waiting to see how the crisis developed before making formal predictions of the losses and that it would be issuing an insured-loss estimate "in the next few days."

Hurricane Katrina cost the insurance industry $41 billion.