Hurricane Harvey is likely to be one of the costliest US natural disasters, according to Impact Forecasting.

For insurers, however, total insured losses are expected to be moderate in comparison with the overall economic cost.

It will take time to assess the final bill as recovery and clean-up operations continue in Texas, which bore the brunt of the Category 4 storm when it made landfall on August 25.

Texas Governor Greg Abbott estimates the damage at $US150-$US180 billion ($188-$226 billion).

The bulk of the insurance cost will probably be met by the National Flood Insurance Program (NFIP), because most of the damage is flood-related.

“Most US homeowners are not insured against flood unless they are located in a flood zone, in which case they often obtain coverage from the government-backed NFIP,” Moody’s Investors Service says.

“While Harvey-related wind damage has been preliminarily estimated in the low billions of dollars, we expect flood-related losses will be much higher.”

“Total insured losses are likely to be moderate relative to overall economic damages.”

Catastrophe modeller RMS estimates NFIP claims from Harvey could reach $US10 billion ($12.6 billion).

Fitch Ratings does not expect downgrades of general insurers or reinsurers as a result of the hurricane.