California wildfires that destroyed about 8900 structures and killed 42 people will cost insurers $US2-3 billion ($2.61-$3.92 billion), according to catastrophe modeller AIR Worldwide.

The loss estimates include residential, mobile home, commercial and motor losses, and direct business interruption.

Residential losses dominate, with several areas such as Sonoma County experiencing catastrophic loss. About 500 of the 100,000 people evacuated remain displaced.

Some 22 wildfires affected almost 100,000 hectares across eight Californian counties from early last month, exacerbated by hot, dry and windy conditions.

Record temperatures were reported throughout Southern California, with Los Angeles exceeding its previous high of 37.2 degrees, set 108 years ago, by hitting 40 degrees.

AIR’s estimate of insured losses is based on an assumption of nearly 100% insurance uptake and the fact wildfire is included in standard homeowners’ policies in California. It does not include losses to land, infrastructure and vineyard crops.